Statistically correlated electrostatic engine diagnostics

ABSTRACT

The categories assigned to waveshapes (FIGS. 57-80) of signals derived from electrostatic probes (1, 2, 3, FIG. 1) disposed in the gas stream of a gas turbine engine are combined over a classification record group of about 20 or 30 records (FIG. 81). The possible causation of signals identified by positive and negative threshold crossings is statistically combined by summation across a group of records (FIGS. 85 and 86). The quality values indicative of the likelihood of a waveform correlating to a catagory of engine event are combined across records, category by category, before decisions are made (FIGS. 87 and 88).

DESCRIPTION

1. Technical Field

This invention relates to electrostatic gas turbine engine diagnostics,and more particularly to improvements in determining engine conditionsas a function of electrostatic phenomena in the gas stream of theengine.

2. Background Art

There are a variety of methods known for generally determining thehealth of gas turbine engines, particularly aircraft engines. Generalengine condition, as well as an indication of engine life expectancy andneed for overhaul, is provided by trending systems which utilize engineparameters such as various temperatures, pressures and controlparameters associated therewith to determine current engine operatingcondition and impute engine health. However, such systems do notrecognize isolated events within the engine which can be indicative ofsevere engine distress or impending engine component failure from aparticular causal event.

Certain engine conditions can be determined visually, such as throughborescopes, without tearing down the engine. As examples, severe bladeerosion (high temperature corrosion), loss of abradable seal segments,or excessive rubbing can frequently be detected by borescope inspectionmethods. Additonally, periodic teardown of an engine allows inspectionof far more components, much more reliably. Because engine teardown issuch a complex and expensive proposition, various schemes are employedto determine when engine teardown should be performed. Tearing enginesdown too frequently is, of course, an extreme waste of time and money.Failure to tear down an engine to determine when it may have problemsthat could result in malfunction or disaster results in enginesmalfunctioning while in use. Because of the complexity and expenseinvolved, any improvement in diagnostic methodology is of great value.

For the past decade, monitoring electrostatic charge in the exhaust gasof a jet engine has been investigated as a possible indication of enginedeterioration and/or impending engine failure. As reported in U.S. Pat.No. 3,775,763, it was originally thought that small particles of engineparts, having a net charge, caused spikes of ion current of relativelylarge magnitude when striking an electrostatic probe. Later, it wastheorized that the electrical activity on ionic probes was the result ofTrichel pulses (a form of repetitive corona discharge) created by highpotential pockets of excess charge, related to engine wear. This isreported by Couch, R. P.: "Detecting Abnormal Turbine EngineDeterioration Using Electrostatic Methods", Journal of Aircraft, Vol.15, Oct. 1978, pp 692-695. A probe set including circular insulatedsegments within the gas turbine engine tail pipe and a triangle of wireextending through the tail pipe exhaust gas path were developed.Oscillograms of typical charge pocket signals observed with the ring andgrid probes are shown in the article. With these probes, a normalizedcount of large signals (probe current, or voltage developed across animpedance, in excess of a threshold magnitude) over a period of timedefinitely correlated with impending engine component malfunctions orsevere deterioration. As reported in the aforementioned article,however, the use of normalized counts of large magnitude signals fromthe ring and grid probe was thought to provide reliable prediction ofonly two out of three gas-path failures, at best, without anydistinction between possible causes thereof. In the article, thenormalized count over a period of time is established as ten times anormal (non-distress indicating) number of threshold exceedances in avariable period of time related to the work done by the engine. Theinterval is determined by D.C. probe current and the square of fan (lowcompressor) speed.

Our commonly owned, contemporaneously filed copending U.S. patentapplication entitled "Waveform Discriminated Electrostatic EngineDiagnostics", Ser. No. 454,124, discloses the correlation betweenparticular events in the engine, some of which are related to specifictypes of engine deteroration, with the wave shapes of electrical signalsgenerated by electrostatic charge in the engine gas stream. However,since randomly occurring engine events are normal (for instance, anoccasional rub means nothing), an improvement to the innovation of theaforementioned Zwicke et al application provides analyzing the resultingwave shapes only when about ten times normal wear occurs within a wearinterval correlated to engine work, as disclosed in a commonly owned,copending U.S. patent application entitled "Expanded ClassificationSample In Electrostatic Engine Diagnostics", filed contemporaneouslyherewith by Couch, Ser. No. 453,967. The improvement therein thusprovides detailed information concerning the events which have occurredduring a time frame where a sufficiently high number of events haveoccurred to be indicative of abnormal wear, and possibly of enginecomponent deterioration, or other events.

DISCLOSURE OF INVENTION

Objects of the invention include improving the correlation ofelectrostatic activity in an engine gas stream with causal eventsoccurring in the engine, and in providing meaningful indications thereofrelated to abnormal wear.

According to the present invention, the correlation by category of agroup of records indicative of electrostatic activity in the gas streamof a gas turbine engine, wherein the group has sufficient number ofrecords therein to indicate abnormal engine wear, is statisticallyclassified by respective, correlated events. More specifically, thepossible categories of causal engine events classified by analysis ofelectrostatic activity are summed across a group of records which isindicative of abnormal wear to determine the most likely category in thegroup, which category is taken as being the causation of the abnormalwear indication.

In one embodiment, the categories of correlated causal events chosen fora number of electrostatic occurrences is arithmetically summed acrosssuch number of occurrences. In another embodiment, the likelihood ofelectrostatic activity at a given probe correlating with a particularengine event, or other condition, is geometrically summed across asignificant number of occurrences of activity.

The present invention provides improved correlation between observedelectrostatic activity and the particular type of engine deteriorationor other event which caused it. The invention may be used with eithersimple or sophisticated category classification systems, utilizingapparatus and techniques which are well within the skill of the art inthe light of the teachings which follow hereinafter.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent in the light of the followingdetailed description of exemplary embodiments thereof, as illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a simplified, sectioned side elevation view of an afterburninggas turbine engine together with a simplified schematic block diagram ofelectrostatic engine diagnostic apparatus attached thereto, in which thepresent invention may be implemented;

FIG. 2 is a simplified, logic flow diagram of a program structure whichmay be utilized in programming a suitable data processing system forimplementing the present invention;

The following are logic flow diagrams of exemplary computer programroutines:

FIG. 3--engine speed request interrupt;

FIG. 4--engine speed ready interrupt;

FIG. 5 and FIG. 6 are illustrative diagrams of data acquisition and datastorage;

The following are logic flow diagrams of exemplary computer programroutines:

FIG. 7--noise interrupt;

FIG. 8--data acquisition interrupt of prior art;

The following are logic flow diagrams of exemplary computer programroutines:

FIG. 9--record classification;

FIG. 10--first probe;

FIG. 11--second probe;

FIG. 12--third probe;

FIG. 13--decision;

FIG. 14--width/peak;

FIG. 15--following peak;

FIG. 16 through FIG. 20 are illustrative waveforms useful inunderstanding the subroutines;

The following are logic flow diagrams of exemplary computer programroutines:

FIG. 21--multiple peaks;

FIG. 22--zero crossings;

FIG. 23--R.M.S.;

FIG. 24--degrade;

FIGS. 25a, 25b, and 25c--narrow pulse;

FIG. 26 through FIG. 33 are illustrative waveforms useful inunderstanding the subroutines;

The following is a logic flow diagram of an exemplary computer programroutine:

FIGS. 34a, 34b, 34c, and 34d--wide pulse;

FIG. 35 through FIG. 42 are illustrative waveforms useful inunderstanding the subroutines;

The following are logic flow diagrams of exemplary computer programroutines:

FIG. 43--surge;

FIG. 44--loose electrode;

FIGS. 45a, and 45b--loose connector/rub strip;

FIG. 46 through FIG. 53 are illustrative waveforms useful inunderstanding the subroutines;

The following are logic flow diagrams of exemplary computer programroutines:

FIGS. 54a, 54b, and 54c--abnormal A/B chop;

FIGS. 55a, and 55b--normal A/B chop; FIG. 56--acel/decel;

The following are diagrams of exemplary waveshapes resulting fromelectrostatic activity in the gas path of the engine, which arediscriminated in this embodiment with the probe (P) and category (C)numbers:

FIG. 57--compressor metal/abradable rub (P 1, C 1);

FIG. 58--compressor metal/metal rub (P 1, C 2);

FIG. 59--surge (P 1, C 3);

FIG. 60--loose probe electrode (P 1, C 1; P 2, C 6);

FIG. 61--loose probe connector (P 1, C 5; P 2, C 7);

FIG. 62--rub strip (P 1, C 6; P 2, C 8; P 3, C 10);

FIG. 63--first high turbine blade erosion (P 2, C 1);

FIG. 64--first high turbine vane erosion (P 2, C 2);

FIG. 65--first high turbine rub (P 2, C 3);

FIG. 66--second high turbine rub (P 2, C 4);

FIG. 67--second high turbine blade or vane erosion (P 2, C 5);

FIG. 68--flaming debris (P 3, C 1);

FIG. 69--A/B nozzle liner erosion (P 3, C 2);

FIG. 70--uncorrelated - 1 (P 3, C 3);

FIG. 71--uncorrelated - 2 (P 3, C 4);

FIG. 72--high turbine rub (P 3, C 5);

FIG. 73--low turbine rub (P 3, C 6);

FIG. 74--high or low turbine impact-induced rub (P 3, C 7);

FIG. 75--high turbine blade erosion (P 3, C 8);

FIG. 76--high turbine vane erosion (P 3, C 9);

FIG. 77--start of abnormal A/B chop (P 3, C 11);

FIG. 78--end of abnormal A/B chop (P 3, C 12);

FIG. 79--normal A/B chop (P 3, C 13); and

FIG. 80--acel/decel (P 3, C 14).

FIG. 81--distress analysis;

FIG. 82-86--second embodiment;

FIGS. 87, 88--third embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Diagnostic System--FIG. 1

Referring to FIG. 1, a plurality of probes 1, 2, 3 are disposed forresponse to electrostatic charge in the gas stream of an afterburninggas turbine engine 4. The engine 4 is shown in an simplified fashion forillustrative purposes only; the invention may be utilized as well withengines which do not have an afterburner, or engines with slightlydifferent characteristics than those implied by the description herein.As shown, the engine 4 has a low pressure spool 6 including a fan 7, alow pressure compressor 8, and a low pressure turbine 9. A high pressurespool 10 includes a high pressure compressor 11 and a high pressureturbine including first blades 12 and second blades 13 (downstream ofand separated from the first blades 12 by vanes, not shown). The probe 2is inserted at the vanes between the high pressure turbine blades 13 andthe low pressure turbine 9. The engine includes an annular burner can 16having dilution air inlet holes 17, 18 therein, the probe 1 beinginserted with its tip in the dilution air inlet hole 17. The core engine6-17 is surrounded by an annular fan duct 20, the outer wall of which isthe engine wall 21. An exhaust cone 23 is supported by suitable struts24. A plurality of spray rings 26 (shown only schematically herein)provide fuel mist to the afterburner of the engine, the essential partof which is a flameholder 27 coupled with an igniter 28. The tail pipeof the engine 30 includes a variable nozzle 31 which is shown in theclosed position herein, but which when moved by actuators, illustratedby an actuator 32, can assume the position shown by the dotted lines 33.The tail pipe 30 has an afterburner liner 34 with a plurality of coolingair outflow holes 35 therein; fan air enters between the liner 34 andthe engine wall 21 in the vicinity of the flameholder 27 to cool theengine wall and avoid burn-through. One of the tests herein isdetermining erosion of the nozzle liner 34. The cooling air continues toflow aft between a balance flap 36 and a movable nozzle liner extensioncalled a balance flap seal 37 which makes rubbing contact with a balanceflap link 38 under which the air flows. Several tests describedhereinafter are related to rubbing of the seal 37 which precedes aburn-through thereof that allows the hot afterburner gases to proceedfrom the tail pipe 30 into the spaces 40 beneath the plate 39, causingnozzle damage.

Each of the probes 1-3 is connected by a suitable conductor 41-43, whichmay preferably be coaxial cable with grounded sheaths, to respectiveterminating impedances 45-47 which may be on the order of 100 kilohms,although the impedance 47 related to the probe 3 may be somewhatsmaller, in some cases, in dependence upon the particular manner inwhich the present invention is utilized. As electrostatic charge passesby any of the probes 1-3, depending upon the polarity of the charge,current flows into and out of the probe, causing corresponding voltagesacross the impedances 45-47. The voltage developed across the impedances45-47 are fed to corresponding amplifiers 48-50, the outputs of whichare fed to corresponding filters 51-53 to have the high frequency, highvoltage Trichel pulses, and other noise signals eliminated. The filterspreferably are band-pass filters having an upper cut-off frequency onthe order of about 600 Hz, although cut-off in the range of 400 to 1,000Hz are suitable. The filters may have a lower cut-off frequency of 1-5Hz, to eliminate some drift and other D.C. phenomenon in the waveshapesbeing examined. In fact, the exemplary waveshapes described herein andillustrated by the exemplars of FIGS. 57-80 were achieved utilizingband-pass filters having a sharp cut-off at 490 Hz.

Each of the filters 51-53 feeds a corresponding analog-to-digital (A/D)converter 54-56 connected with a signal processing computer 60. Asdescribed more fully hereinafter, the A/D converters are operated tosample the filter outputs (the probe signals) once about everymillisecond, the A/D converters being read in rapid succession, withinabout 10 microseconds of each other. However, the exemplary waveformsillustrated in FIGS. 57-80 herein were obtained by sampling at a 1.3 KHzrate. And the parameters given for use in various subroutines todiscriminate the various waveforms from each other set forth in Tables2-9 hereinafter are related to the utilization of the 1.3 KHz rate,there being 26 historical samples prior to the sample which crosses athreshold (as described hereinafter) in a 20 millisecond history periodand 77 additional samples across a 60 millesecond post thresholdcrossing interval, totaling 104 samples in an 80 millisecond recordwhich each of the waveshapes of FIGS. 57-80 comprise.

For pockets of sufficient charge to be of interest, current in the probe1 may be on the order of 0.10 microamperes; current in the probe 2 maybe on the order of 0.20 microamperes; and current in the probe 3 may beon the order of 2.5 microamperes. Within impedances of about 100kilohms, the gain of amplifiers 48 and 49 may be about 100, and the gainof amplifier 50 may be about 10. This results in signals of interest ofbetween one and ten volts, with an occasional higher signal. The D/Aconverters need only respond to 10 volts, any saturation from highervoltages being unimportant. With the aforementioned gains, thresholds(described with respect to FIG. 8, hereinafter) may be 1 volt for probe1, 2 volts for probe 2 and 21/2volts for probe 3, if fixed thresholdsare used. This, of course, will vary depending on how the invention isutilized. If desired, the impedances and voltage scaling can be changedto suit different A/D converters.

The signal processing computer 60 may also have an R.M.S. A/D 62, theinput of which is a conventional R.M.S. detector 63 which is connectedto the probe 3 because probe 3 has no contact with the engine exhaust,and therefore has no D.C. component and very low noise, as described inthe aforementioned Couch application, Ser. No. 453,967. The R.M.S.detector preferably includes, or is fed by, an isolation amplifier (notshown). As described hereinafter, R.M.S. noise is utilized in thepresent embodiment as an indicator of a normal wear interval. The signalprocessing computer 60 may also have an engine speed input on a line 64provided by a tachometer 65 responsive to the low pressure spool 6 (N1).In the present embodiment, the engine speed signal is used to provide anacceleration variation of threshold. The signal processing computer 60may also be provided with a signal on a line 66 provided by a powerlever angle transducer 68. In the present embodiment, this simplyprovides historical information to accompany the data which is otherwiseacquired and analyzed. The signal processing computer 60 may haveconventional input/output devices attached thereto in order to derivethe useful information provided thereby: these may include a keyboard70, a printer 71, a display unit 72 and a recording device 73, such as amagnetic floppy disc or a magnetic tape cassette, or the like, asdesired. If the invention is utilized in an airborne environment(necessitating use of a different probe than the hoop probe 3), theconventional input/output devices 70-73 would not be used; instead, anonvolatile storage module would be used to collect data in the air, thecontent of which would be displayed and analyzed in ground-base signalprocessing apparatus.

The signal processing computer 60 may be selected from a wide variety ofcommercially available signal processors. Such computers may be as smallas an Intel 8080, or may be larger, such as the Texas Instruments 9900series. Or, in dependence upon the speed and amount of information whichis desired to be retained during any given operation, a mini-computersuch as a Digital Equipment Corp. PDP/11 series may be used. Of course,any larger computer may be used if desired. Or, two microprocessorC.P.U.s may be used: one for data acquisition and one for date waveformclassification and/or analysis. The particular nature of the particularcomputer used, the input/output equipment disposed thereon, samplingrates and other things can be varied to suit any implementation of thepresent invention, utilizing readily available hardware and suitablecommon programming techniques, which are well within the skill of theart in the light of the teachings which follow hereinfter.

In the description which follows hereinafter, it should be understoodthat various features set forth and claimed in other commonly owned,copending U.S. patent applications are disclosed. These are disclosedherein for simplicity in illustrating the best mode of the presentinvention, which may be utilized in conjunction with such otherfeatures, and for simplicity in presenting the manner in which the otherfeatures may be incorporated herewith. However, the present inventionrelates to the discrimination by waveshape of electrical signalsproduced by electrostatic effects in the engine gas stream, and whichcorrelate in major part with known events or conditions of the engine.

Abbreviations, some or all of which are used herein, are set forth inTable I.

                  TABLE I                                                         ______________________________________                                        A/B = afterburner  MEASRD = measured                                          ABNORML = abnormal MIN = minimum                                              ABSNT = absent     MULT = multiple                                            ACEL = acceleration                                                                              NEG = negative                                             A/D = analog-to-digital                                                                          NOMNL = nominal                                            ADV = advance      OPOS = opposite                                            BEG = beginning    P = PROB = probe                                           BUF = buffer       PARAM = parameter                                          C = CAT = category PK = peak                                                  CLAS = classification                                                                            P.L.A. = power lever angle                                 CONECTR = connector                                                                              POST = post-pulse                                          CROS = CROSNGS = crossings                                                                       PRE = pre-pulse                                            CTR = counter      PRIM = primary                                             DECEL = deceleration                                                                             PROG = progress                                            DECR = decrement   PTR = pointer                                              DGRD = degrade     PULS = pulse                                               DGRDN = degradation                                                                              Q = quality factor                                         DIF = difference   R = RCRD = record                                          DISTRS = distress  RDY = ready                                                DVSR = divisor     REQ = request                                              ENBL = enable      REVRS = reverse                                            ENG = engine       R.M.S. = root-mean-squared                                 EXP = exponent     RSLTS = results                                            FLG = flag         RST = reset                                                FOLWNG = following S = SAMPL = sample                                         FXD = fixed        SENSTVTY = sensivity                                       G = group          SEPRATN = separation                                       HI = high          SIN = sign                                                 HISTRY = history   SPD = speed                                                INCR = increment   SQRT = square root                                         INIT = initialize  STR = store                                                INTGRL = integral  STRT = start                                               INTVL = interval   TACH = tachometer                                          IRPT = interrupt   THRSH = threshold                                          LIM = limit        V = value, volts                                           LO = low           VARIATN = variation                                        MAX = maximum      ( ) = of; or grouping                                      ______________________________________                                    

Program Structure--FIG. 2

Referring now to FIG. 2, a simplified illustration of an exemplaryprogram structure for acquiring and classifying data provided from theprobes 1--3 disposed for response to the engine includes utilization ofinterrupts to acquire data and utilization of background programs (whichmay be interrupted for data acquisition) for classifying, analyzing, andcorrelating the data. The program structure is exemplary merely, andother structures may be utilized in dependence upon the size and type ofdata processing system used to implement the present invention.Typically, systems are initialized on power-up by a power-up interruptroutine 1 which is automatically reached by the highest orderedinterrupt in an interrupt priority scheme. Other interrupts 2 may beutilized, such as for sending and receiving data to auxiliary storagedevices (such as cassettes and floppy discs) or sending data to aprinter. Then a medium priority interrupt 3 may reach an engine speedready interrupt program to read engine speed, as described more fullyhereinafter with respect to FIG. 4. A next higher order interrupt 4 mayreach a data acquisition interrupt program for actually reading the datafrom the probes disposed with the engine, as is described more fullyhereinafter with respect to FIG. 8. And an interrupt 5 of a relativelylower priority may reach an engine speed request interrupt program, forinitiating the reading of engine speed, as described with respect toFIG. 3 hereinafter. A relatively still lower priority interrupt 6 mayreach a noise interrupt program for reading R.M.S. noise on one of theprobes, as is described more fully hereinafter with respect to FIG. 7.Then, other interrupts 7 of still lower ordered priority may be utilizedsuch as to control tape transport real time delays and to handle displayand keyboard character exchange. All such other interrupts are thosewhich will suit any given implementation of the invention, in dependenceupon the particular system in which the invention is embodied and thedesign requirements thereof.

In FIG. 2, as an example only, a record clasification program, describedin detail with respect to FIG. 9, is called on a regular basis, and isactually performed whenever records have been accumulated to beclassified and the classification has not yet been done (as describedhereinafter). Briefly illustrated is the basic units of the recordclassification program of FIG. 9. For instance, the recordclassification program 8 includes a first probe subroutine 9 whichcompares a sample record with five categories of signals, followingwhich a decision subroutine 10 determines which of the five categories(if any) is likely to have been the one which occurred in the engine.Then a second probe subroutine 11 examines a record against thecharacteristics of seven categories and a decision subroutine 12determines which of the seven categories is likely to have occurred inthe engine. A third probe subroutine 13 examines the records from thethird probe against characteristics of fourteen different categories anda decision subroutine 14 determines which of the fourteen categories (ifany) is likely to have occurred in the engine. The process set forthillustratively with respect to the subroutines 9-14 is repeated until anindication 15 is provided that an entire group of records has beenclassified. Then, a distress analysis program 16 may be called toprovide further, post-classification processing in a manner describedmore fully hereinafter with respect to FIG. 9 hereinafter. Thus, asrecord classification and distress analysis are being performed,acquisition of probe data, engine speed and noise continues by means ofinterruption of the record classification and distress analysisprograms.

Engine Speed--FIG. 3., FIG. 4

Referring now to FIG. 3, an engine speed request interrupt is issued ona real time basis, such as twice per second. This reaches an enginespeed request interrupt program through an entry point 1 in FIG. 3. Apair of steps 2 cause an engine speed counter to be reset to all zerosand a tachometer I/O request to be issued. Then, a test 3 determineswhen the tachometer I/O has acknowledged the request with a handshake,and when it does, an affirmative result of test 3 reaches a pair ofsteps 4 in which a speed timer is started and the engine speed readyinterrupt is enabled (if required). Then the program ends at point 5 andthe program which was interrupted (if any) is resumed through ordinary,interrupt handling processes. When the speed timer started in steps 4 ofFIG. 3 reaches a predetermined count (across which tachometer pulses arecounted by the engine speed counter which was reset in steps 2), thespeed timer will then issue an engine speed ready interrupt.

In FIG. 4, the engine speed ready interrupt reaches an engine speedready interrupt program through an entry point 1. In a series of steps2, the engine speed information is processed so as to provide a voltagethreshold for one of the probes (such as the third probe in the presentembodiment) which includes a component related to engine speed. In thesteps 2, new engine speed (designated by "n") is set equal to the enginespeed counter. The faster the engine was going, the higher the count.Then engine acceleration is determined by subtracting the old enginespeed (designated by "m") from new engine speed. Then the threshold forthe third probe is provided by multiplying the absolute value of engineacceleration (so as to be positive during either acceleration ordeceleration) by some constant, and adding it to a fixed threshold valuewhich is otherwise appropriate for that probe. Then the old engine speedis updated by making it equal to the new engine speed. Engine speed (orthe preceding sequence of speeds) can also be recorded as one of theparameters in a record indicative of an event in the engine, asdescribed hereinafter. This poses no problem since the new value ofengine speed can be reached in a steady condition (not changing from oldvalue to new value) at all times other than during the engine speedready interrupt. When the steps 2 have been performed, the program isended through an exit point 3. Then, any program which was interruptedby the engine speed ready interrupt is reverted to through ordinaryinterrupt handling processes. Engine speed may alternatively be derivedusing automatic hardware apparatus, rather than a clocked interrupt.

Illustration Of Data Acquisition--FIG. 5, FIG. 6

The manner in which the data acquisition interrupt 4 of FIG. 2 acquiressamples from the probes is illustrated briefly at the bottom of FIG. 5.In FIG. 5, each of the probe A/Ds is interrogated once about everymillisecond. During acquisitions of the data, the A/Ds for thesuccessive probes are read in the order: probe 1, probe 2, probe 3.These are read as quickly as they can be (as closely as possibletogether) so that the data samples (1-104 in the present embodimentexample) will relate very closely to the same time frame and thereforehave correlative meaning. A sample rate on the order of 1000/second (1millisecond between samples) has been found to be acceptable. Thisleaves approximately 750 milliseconds for processing (such as recordclassification and the like) as described with respect to FIG. 2hereinbefore, between the sampling of triplets of data from the probes.As each probe is sampled, the digital value indicative of the magnitudeof signal on the probe (illustration (f), FIG. 6) is stored in acorresponding, successive location in a portion of storage referred toherein as a history buffer (illustration (e), FIG. 6). The historybuffer may have the capacity to hold 32 or 256 (or some other number of)triplets of data as illustrated in the bottom of FIG. 6. Therein, thedata samples for probes 1-3 are indicated as having been stored inpositions of the history buffer arbitrarily identified as numbers 31through 62. The reading of data from the A/Ds into the history buffergoes on continuously, without regard to whether or not thresholds havebeen exceeded. When the history buffer is full, the correspondinghistory buffer pointers (one for each probe) simply cycle around to thelowest address thereof and continue to overwrite data in a cyclicmanner. This data is of no significance except in the event that thevalue sensed on one of the probes exceeds the threshold for that probe;a threshold exceedance at any one of the probes causes the last 27samples for all of the probes to be moved from the history buffer(illustration (e) of FIG. 6) into the record buffer (illustration (d) ofFIG. 6). The record buffer is shown in an expanded format, andillustrates that 104 samples and other data relating to each probe, aswell as additional data such as speed, power level angle and time, maybe stored in each record which results from each threshold exceedance byany one of the three probes. The sample value number (1-29 . . . 104)thus becomes known only once a threshold is exceeded by the data sensedon one of the probes. The bottom portion of illustration (d) of therecord buffer shows an exemplary complete record, identified as recordnumber 61 in the middle portion of illustration (d) in FIG. 6. Capturinga complete record whenever an event occurs in the engine as sensed onany one of the three probes, does not necessarily result in utilizationof any of that data. This is because events occur occasionally even in ahealthy engine, so analysis of the particular event is not necessarilyan indication of abnormal engine wear. Instead, abnormal wear isindicated by the occurrence of some large number of thresholdexceedances (such as ten times a normal number) within a given wearinterval of time (which may be a fixed or variable interval of time). Inthe present embodiment, the wear interval is variable and is dependentupon the average value of R.M.S. noise on one of the probes at timesother than when an event is occurring, as is described more fully withrespect to FIG. 7 hereinafter. In the present embodiment, "M" isdetermined to be ten times the normal number of threshold exceedanceswhich should occur during a wear interval in a healthy engine. Thisnumber may be, for instance, on the order of 20 or so. The value "N" istaken to be some arbitrary number of additional records, following theoccurrence of ten times normal wear, which may be taken so as tocomplete a classification group of records to provide an indication ofwhat sort of abnormal wear has occurred. In the present embodiment, Nmay be on the order of ten or so. As shown in the middle of illustration(d) of FIG. 6, a group of records is composed of M+N records numbered 60through 90 totaling thirty records and comprising group 2. Groups 1-4 ofthe record buffer are shown in the upper portion of illustration (d).These groups of records are stored away in a fairly substantial recordbuffer which may contain on the order of 64 or 256 records. Dependingupon the particular manner in which the present invention is utilized,records may be accumulated until the record buffer is full, after whichno more records are taken. Or, the record buffer may be operated in acyclic fashion (as described with respect to the history bufferhereinbefore) so when the maximum address for the highest group ofrecords is reached, the pointers (R, R') which keep track of the recordbuffer revert to zero and begin to walk through the record buffer asecond time. In the present embodiment, a cyclic record buffer of asuitable size is presumed to be desirable and provisions are made toprevent records from being overwritten until the data content thereofhas been analyzed. In such a case, the results of analysis for anyparticular group of records may be stored in a group results portion ofstorage as shown in illustration (a) of FIG. 6. The amount of storagerequired to store the overall processed results for each group isextremely small compared to all of the sample records in each of thegroups, and therefore a significantly large number of group results canbe stored with relatively small amount of storage. In other embodiments,the classification may be done either off-line or in separate equipment(such as when data is collected by an airborne data acquisition unit andprocessed in a ground based classification unit). In such a case, therecord buffer is preferably comprised of a nonvolatile storage, and whenthe record buffer is full with some reasonable number of groups ofrecords, acquiring of further records ceases, as described more fullyhereinafter. Other aspects of storage which are illustrated briefly inFIG. 6 are described hereinafter.

In FIG. 6, the groups 1-4 of records are shown as stored contiguously inthe record buffer. However, the present embodiment retains records onlyin the event that M records occur within a wear interval. If a fewernumber of records occur during a wear interval, this is taken to benormal wear and not worthy of being recorded. However, it cannot beknown whether or not M records will occur during the wear interval untilM number of records have been collected prior to completion of a wearinterval.

Referring to the top of FIG. 5, four groups of M+N records are shown.The first group of records was started at some arbitrary point withinthe first wear interval. Since M records were accumulated before the endof the wear interval, a distress threshold (M) was exceeded and N morerecords were accumulated, even though some of these were accumulated ina following wear interval. At the time that M1 set of records werecompleted, the M counter was reset and additional records are collectedin the N1 set; these records are also designated (simply by themechanisms described hereinafter) as being applicable to the secondgroup of records. But just after starting to collect the second group ofrecords, the end of the first wear interval caused resetting of the Mcounter again so that counting of M records commenced anew (designatedM2' in FIG. 5). Some of these records are the same records as areutilized in group 1 as well. Eventually M2' reaches the distressthreshold and M is reset once again. The N2 set of records are collectdto finish the second group of records and some of these records aredesignated for the third group as well (M3 in FIG. 5). But before adistress threshold is reched for the third group, the end of the secondwear interval occurs and resets the M counter again. Thus the taking ofrecords for the third group of records commences anew at the begining ofthe third wear interval. As it were, the entire third wear interval didnot have sufficient records to exceed the distress threshold in theexample of FIG. 5, so the M counter is reset again at the end of thethird wear interval. Beginning the the fourth wear interval, another setof M records is started for the third group (M3"). In the example ofFIG. 5, apparently a large amount of activity occurs during the fourthwear interval so that M records are collected early in the interval anda fourth group is started. The third group is completed and M recordsfor the fourth group are completed prior to the end of the fourthinterval so that in fact two groups are completed mainly within thefourth wear interval.

Notice that the wear intervals are not of the same time duration: thatis because in the present embodiment the wear intervals are determinedby R.M.S. noise of the engine. Since the electrostatic noise effluent inan engine is very closely a linear function of engine wear, thisprovides a manner of indicating how much activity should occur in agiven period of time to separate normal activity from abnormal wearactivity.

In FIG. 5, notice that when the N sets of records to complete a grouphave been taken, this does not affect the allocation of some of thoserecords to an M set for a following group. Notice also that the Mcounter is reset so as to start a new count at the end of each wearinterval, but the records collected thereafter will be for the samegroup of records that has just been terminated. On the other hand,whenever a distress threshold is exceeded (that is M, number of recordshave been collected) not only is the M counter reset so as to start anew group, but N more records are collected for the current group. Thetime interval required for M or N thresholds is also variable, dependingon how much activity there is in the engine. This is illustrated best inFIG. 5 by comparison of the third and fourth interval wherein muchactivity occurred in the fourth interval so that two records could bedesignated while at the same time insufficient records were created inthe third interval so as to declare a record.

R.M.S. Noise, Wear Interval--FIG. 7

Referring now to FIG. 7, the reading of R.M.S. noise from one of theprobes and the provision of an R.M.S. noise wear interval (andaccommodating the consequences thereof) is illustrated in an exemplaryfashion. The noise interrupt 6 of FFF. 4 reaches the noise interruptprogram of FIG. 7 through an entry point 1 andna first pair of tests 2,3 determine if a record is in progress or not. If a record is inprogress, it is because one of the probes has had a threshold exceedancewithin about 70 milliseconds of the noise interrupt. The thresholdexceedance, being an abnormal event, is not indicative of ordinaryR.M.S. noise currently in the engine. Therefore, a reading of R.M.S.noise is not made in the case where a record has been initiated or isstill in progress as indicated by the tests 2, 3. But whenever a recordis not in progress, negative results of steps 2 and 3 in FIG. 7 willreach a step 4 wherein the R.M.S. A/D 62 is started. Then a test 5determines when the R.M.S. A/D is complete so that an R.M.S. value canbe stored in a step 6. Whenever a record has been initiated or is inprogress, the R.M.S. value previously stored in step 6 is not disturbeddue to bypassing thereof by affirmative results of either test 2 or 3.

In FIG. 7, a step 7 provides an R.M.S. increment as the differencebetween the stored R.M.S. value and some R.M.S. threshold. The R.M.S.threshold is a value of electrostatic noise at the probe (e.g., thehoop, probe 3 in this embodiment) which is very low, and indicative ofthe normal noise level during low thrust operation of a healthy engine.The R.M.S. threshold can be chosen as being some value of R.M.S. noisewhich is sufficiently low that the contribution it would make (during ahalf-second of time) can be ignored completely in the R.M.S. interval.This makes a wear interval dependent only on excessive R.M.S. noisewhich therefore is more sensitive to current engine conditions. Thus ifan engine has a relatively high normal noise level, the wear intervalsneed not necessarily be unduly short, thereby causing an excessiveamount of uninteresting data to be accumulated; instead, the R.M.S.threshold for reading that particular engine can be raised, therebyproviding a meaningful wear interval based on R.M.S. noise, even thoughR.M.S. noise (at a given power level) may vary considerably from oneengine model to the next (or even from engine to engine of the samemodel), which is not likely. In FIG. 7, if the R.M.S. noise is greaterthan the threshold, an affirmative result of test 8 will reach the step10 in which an R.M.S. integral is incremented by some constant times theR.M.S. increment. This is a typical integration function, except for thefact it is only performed if the R.M.S. noise exceeds the R.M.S.threshold.

In FIG. 7, the R.M.S. integral is compared against some basic wearinterval in a step 12. The wear interval is not a unit of time, butrather a unit indicative of a variable period of time within which theengine will exert a certain amount of work (power for a period of time),in relation to the total work the engine may exert during normal enginelife. The interval corresponds to a short flight or a half-hour test;ideally, it represents about three cycles of start-up, advance tomaximum power, and shut down. The wear interval is described in terms ofpower and cycling in the aforementioned Couch article. During thevariable wear interval, a given engine will have a normal amount ofactivity, such as the collection of two records (two events resulting inthreshold exceedance), whereby the collection of ten times that numberof records (such as 20) will be indicative of abnormal wear. If theR.M.S. integral has not exceeded the wear interval value therefor, anegative result of test 12 will reach the program end at a point 18.Similarly, if test 8 determines the increment to be negative, thesubroutine not only bypasses step 10, but it bypasses the remainingsteps since the wear interval (having not been exceeded in a prior passthrough the subroutine) could not be exceeded with the unchangedintegral. However, whenever the R.M.S. noise has integrated to a pointwhere it exceeds the wear interval, an affirmative result of test 12will reach a series of steps 13 in which the M counter is set equal tozero and an I pointer is incremented. The I pointer incremented in step13 of FIG. 7 is utilized as an address component for distress countersin storage which are shown in illustration (b) of FIG. 6. As decribedmore fully hereinafter, a threshold exceedance in the positive directionor in the negative direction for each of the probes connected with theengine is counted separately during each wear interval, and these countsmay be saved as an indication of the temporal spectrum of wear whichoccurred (without regard particularly to what caused it in the generalcase) during the operation of the engine. Thus, in the course of fortyhours of flying time, patterns of excessive wear indicated only by thesecounters will generally show increases in count in a sustained fashionwithin a period of time (e.g., tens of hours) just before severe enginedistress could otherwise be noticed, such as by adverse operation,borescope inspection or the like.

In FIG. 7, a test 14 determines whether a distress flag has been set ornot, described more fully hereinafter; the test 14 relates to whether ornot M records have been sensed within a single wear interval, as isdescribed with respect to the top of FIG. 5 hereinbefore. If M recordshave been collected during the wear interval, (such as at the end ofinterval 1, interval 2 and interval 4 in FIG. 5) then the first recordin the next group (such as M2' in FIG. 5) will begin at the point in therecord buffer where records are now being stored. Thus an affirmativeresult of test 14 will reach a step 16 wherein a temporary pointer(called Begin M) is set equal to the current value of an R pointer thatkeeps track of records being stored in the record buffer (illustration(d), FIG. 6). On the other hand, if distress has not been indicated (thedistress threshold M not having been exceeded), different operationoccurs. This is the case illustrated at the end of the second and thirdwear intervals at the top of FIG. 5. At the end of the second wearinterval, the record buffer has been filled with M2' and N2' and thusstoring of new data not related to the second group should begin at theend of the second group. But, the record buffer has been filled withsome number of records designated as X.S. in the top of FIG. 5 which areof no value since they did not amount to an excessive number within thewear interval. These may be thrown away and therefore they may bewritten over by the third group. Therefore, the designation of the pointin the record buffer where the third group of records may occur is alower address number than the current address being used in storing ofM3, at the end of the second wear interval.

With these factors in mind, a series of steps 17 in FIG. 7 will cause anR decrement to be generated equal to the difference between an R pointerand an N pointer. The R pointer is the current address being used tostore the M3 records at the end of the second interval. The N pointer isa saved address indicative of the last address utilized in storing theN2 records of group 2. This allows sliding the record buffer addressback so that the third group can be contiguous with the end of thesecond group. Then an R counter (a count which continues upwardly,rather than recycling back to a low address value as the R pointer does)is decremented by having the R decrement subtracted therefrom. The Rpointer is then updated to equal the N pointer, thereby causing theaddress for the first record of the third group to be next higher thanthe address of the last record of the second group. And the beginningaddress for the particular group of records is recorded as being equalto the R pointer. Then the noise interrupt program of FIG. 7 ends atpoint 18, and any other program which had been interrupted thereby isreturned to utilizing ordinary interrupt handling processes.

Data Acquisition--FIG. 8

Referring to FIG. 8, a real time interrupt, once each millisecond,causes the sampling of all of the probes on the engine at the onekilohertz data acquisition rate. Ideally, the probes will be sampledsimultaneously. But, hardware constraints, such as use of a singlemultiplexed A/D, or a single A/D bus system, may require successivesampling. In this embodiment, during each interrupt, all of the probesare sampled about one-tenth of a millisecond apart from each other. Thedata acquisition interrupt is reached through an entry point 1 in FIG.8, and a first test 2 determines whether data acquisition operation hasbeen initiated or not. Upon initial power-up, a negative result of test2 will cause a series of steps 3 to: reset a group counter (G) to "one"(indicating that there has not as yet been collected a first group ofthreshold-exceeding samples indicating ten times normal wear); reset agroup counter (G') to one (indicating that a first group of records hasnot yet been classified); reset a record pointer (R PTR) to "one"(indicating that the first record is about to be made as a consequenceof one of the probes having a signal magnitude in excess of the recordthreshold); set a probe pointer (P) to the highest-numbered probe (3 inthe present embodiment) so that when advanced, the probe pointer will bepointing at the first probe; set I=1 (indicating the first wear intervalis about to start); reset M and N to zero; and set the initialize flag.In all passes through data acquisition interrupt program of FIG. 7,subsequent to the first pass on power-up, the results of test 2 will beaffirmative, thus bypassing the initializing steps 3.

Routine Sampling of Data

Once initialized, the iterative steps of the data acquisition interruptprogram continue with steps 4 in which the P pointer is advanced and theA/D for probe P is started, after which a test 5 determines whether theA/D converter related to the probe identified by P pointer has completedthe conversion, or not. The program hangs up on test 5 until the A/Dconverter for the P probe is complete, after which an affirmative resultof test 5 reaches a series of steps 6 in which the A/D converter for thenext probe (one in advance of probe P) is started, the history bufferfor probe P has stored in it the A/D results from the A/D converter forprobe P, and the history buffer pointer (designating the particular partof the cyclic history buffer) for probe P is advanced. The historybuffer for each probe may be of any desired size, but in the exampleherein they must have at least 27 sample storage locations each, sincethe records of the present embodiment include 27 samples of historyalong with 77 samples which are captured on-the-fly following athreshold exceedance. Thus any available memory locations may beutilized as history buffers by means of address portions relating to thehistory buffer as a whole, address portions relating to the particularprobe involved, and address portions corresponding to the historypointer for the particular probe (the probe's portion of the historybuffer).

In FIG. 8, for each sample read into the history buffer in the steps 6,a test 7 determines whether a record is already in progress or not. Ifnot, a negative result of test 7 reaches a test 8 which determines if arecord has been initiated or not. The initiation of a record, asdescribed below, occurs whenever a threshold is exceeded (on any one ofthe probes) for the first time following the completion of a previousrecord. A negative result of test 8 will reach a test 9 which determinesif the last sample to be read exceeds the negative threshold for thisprobe, or not. If not, a test 10 determines if the most recent sampleexceeds the positive threshold for this probe. If the most recent sampledoes not exceed the record threshold in either the positive or thenegative direction, negative results of tests 9 and 10 combine to reacha test 11 to see if the third probe has been read during this iteration.If not, a negative result of test 11 returns the program to step 4 tocause reading of the next sample, and starting the A/D converter for thesample following the next sample. When all three probes have beensampled, an affirmative result of test 11 will reach a test 12 to see ifa record has been declared. Since threshold exceedances only occur sometens of times per million interrupts, usually no record is declared anda negative result of test 12 reaches the program end point 14.

In cases where none of the samples exceed the threshold, passage throughsteps and tests 4--11 three times, (with the A/D converter for eachprobe being read once and the results thereof stored in thecorresponding history buffer for the probe) and ending through test 12is all that occurs. This can go on virtually indefinitely in subsequentpasses through the data acquisition interrupt routine, so long as nothreshold is exceeded. In such a case, all that occurs is that data isstored in the history buffer in a cyclical fashion. When each historypointer reaches maximum and returns to a minimum setting, the newlyincoming data will simply be overwritten over the oldest data in thehistory buffer, in a cyclical fashion.

Declaring a Record

Eventually, one of the three probes may provide a signal in excess ofits record threshold so that one of the tests 9, 10 in FIG. 8 will beaffirmative. It does not matter which of the three probes does this; inany event a record is declared as a consequence of one of the threeprobes having a signal in excess of either its positive or negativethreshold. In such a case, an affirmative result of test 9 will cause astep 15 to increment the negative distress counter for probe P withinthe current alarm interval (I) storage area. Or, an affirmative resultof test 10 will cause a step 16 to increment a positive counter. Then, aseries of steps 18 will record the source of the exceedance as thecurrent probe, store the current threshold values for all three probes,and set the record initiated flag. If the first or second probe causedsetting of the record initiated flag in steps 18, test 11 will again benegative so the program will return to step 4 until all three probeshave been read during the present cycle. Once all three probes have beenread, then tests 11 and 12 will be affirmative causing the program toadvance to a test 19 to ensure that storage of a record at R in therecord buffer will not write over a record that has not already beenclassified. In test 19, R Max is the total number of records that can bestore; the R counter keeps track of how many have been stored; and theR' counter keeps track of how many have been classified (and analyzed,if post classification analysis is utilized). If the buffer is full, anegative result of test 19 will reach a step 20 which resets the recordinitiated flag, thereby causing the record to become undeclared. If thebuffer is not full, an affirmative result of test 19 reaches a series ofsteps 21 which initialize moving the history buffer for one of theprobes to the record buffer for that probe.

Moving the History Data

Specifically, in steps 21, the P pointer is advanced (so during thefirst pass it will point to the first probe); the end of the history forthe present record for the particular probe is stored as being equal tothe current setting of the history pointer for that probe; thismemorizes the point at which taking the history from the history bufferand putting it in the record buffer will be complete as describedhereinafter; then the history pointer for the present probe isdecremented by 26 samples so as to go back to a point in the historybuffer which will include 27 samples of the present record (the pulsewave shape to be stored as a consequence of the last triplet of incomingdata including one data magnitude which exceeded a threshold). Then in aseries of steps 23, one sample of the record buffer for the currentrecord, R (which is initialized as the first record in the steps 3),relating to the current probe, P, is set equal to the sample in thehistory buffer being pointed to by the history pointer. In the firstpass through the steps 23, the first sample of the history buffer forprobe 1 is moved into the first sample of the record buffer for probe 1,for the first record. Then the record buffer pointer for probe P isadvanced and the history pointer for probe P is advanced. Then, in atest 24, it is determined whether or not all of the history has beenmoved into the record buffer for this particular probe by comparing thepresent state of the history pointer for probe P with the maximumhistory previously stored for probe P. If the complete history has notbeen moved to the record buffer, a negative result of test 16 causes thesteps 15 to be repeated for successively advancing samples of thehistory buffer and the record buffer. Eventually, all of the history forprobe P will have been moved to the record buffer for the first recordfor the first probe, in which case a negative result of test 24 willreach a test 25 to determine if all three probes have completed movementof samples from their history buffers to their record buffers.Initially, since the first probe has its history moved to the recordbuffer first, P will equal 1, so a negative result of test 17 will causethe steps and tests 21-25 to be repeated for the second probe andultimately for the third probe. When the history for all three probeshas been moved to the record buffer, an affirmative result of test 25causes a series of steps 26 to be reached: a sample counter is set to 77(indicative of the 77 samples of the record for each probe to be takendirectly into the record buffer, as well as being stored in the historybuffer); and, a record in progress flag is set and the record initiatedflag is reset. At the conclusion of steps 26, the end of the program isreached at the point 14.

Capturing the Remaining Record On-The-Fly

In FIG. 10, the next time a data acquisition interrupt occurs, theresult of test 2 will be affirmative, bypassing the steps 3 sinceinitialization has already occurred. Once a threshold has been exceededand a record declared, the next subsequent data acquisition interruptwill cause the routine of FIG. 8 to pass through an affirmative resultof test 2 to the step 4 and P is advanced from the third probe to thefirst probe once again, and the A/D for the first probe is started. Assoon as test 5 is affirmative, a series of steps 6 start the nextsubsequent A/D, store the current sample in the history buffer for thepresent probe, and advances the history buffer pointer for that probefor use in the next cycle. Now, however, test 7 will be affirmativebecause there is a record in progress (one of the previous sampleshaving exceeded a threshold).

An affirmative result of test 7 in FIG. 8 reaches a pair of steps 30 inwhich the record buffer for the first record and the first probe is setequal to the A/D result for the first probe and the record bufferpointer for that probe is advanced for use in a subsequent cycle. Then atest 31 determines if all three probes have been sampled in thisparticular pass through the data acquisition interrupt program of FIG.8. If not, the program reverts to step 4 to handle the sample of thenext probe in sequence until all three probes have had their A/D samplesread into the record buffer, and the record buffer pointer therefore hasbeen advanced. When all three probes are complete, an affirmative resultof test 31 reaches a step 32 which decrements the sample counter andthen a test 33 which determines if the sample counter has reached zero,indicating that 77 samples subsequent to a threshold exceedance havebeen stored for all three probes. If not, the program ends at the point14 for the current interrupt.

Successive data acquisition interrupts cause the program of FIG. 8 tocontinue to pass through the steps and tests 4-7 and 30-33 until,finally, the sample counter has been decremented from 77 all the way tozero. This indicates that 77 samples have not only been put into thehistory buffer but have been placed directly in the record buffer aswell, for each of the three probes. This means that the record buffernow contains the original 27 samples transferred from the history bufferin steps 21 and 23 and the additional 77 samples taken directly into therecord buffer in steps 30. During this time, the history buffer ismaintained up-to-date in step 6 so that whenever there is a subsequentexceedance, the history will be available.

Completing a Record

Eventually, when all 77 on--the--fly samples have been stored in steps30 of FIG. 8, for all three probes, an affirmative result of test 33reaches a series of steps 35 in which the speed to be recorded with thisrecord is set equal to the current engine speed (FIG. 4); the powerlever angle (P.L.A.) for the record is the current value (not shown);the time is the current time; the record pointer (R PTR) is incremented(since a complete record of triplets of 104 samples each has beencompleted); the corresponding R counter is incremented (this keeps trackof the total number of records stored, even after the R PTR reverts tothe lowest address); a temporary count (M) of records is incremented(for use as described with respect to FIG. 5); and the record inprogress flag is reset. If desired, a history of engine speed over thelast 5 seconds or so may be recorded, for print-out with classificationresults, to aid in subsequent operator interpretation of engineconditions.

Testing for Abnormal Wear

In FIG. 8, a test 36 determines if a distress flag is set (as describedhereinafter). Initially it is not, so a test 37 is reached wherein thenumber of records M (the number of times that a threshold exceedance hasrecently occurred) is compared against a distress threshold. Asdescribed briefly hereinbefore, the distres threshold is preferablytaken to be some value on the order of ten times the normal amount ofrecords which may occur in a healthy engine during a given test, flight,or other distress-related interval of time. The distress threshold isset equal to some given number of counts such as 20 or 30 counts. Thedistress threshold test 37 simply compares the number of records whichhave been taken since the last indication of distress or since the startof the current wear interval, with the number of records which areindicative of a distress value of wear (a unit of distress). In the caseof the first few records taken, the result of test 37 will be negativecausing the program to end at point 14.

Thus, as a consequence of having one probe sample exceed the threshold,a record of 104 samples for each of the three probes (along with otherdata) will have been placed in the record buffer and the record pointerincremented. Then, in a subsequent data acquisition interrupt aftercompletion of the record, data acquisition continues as describedhereinbefore. Ultimately, when some number of records indicative ofdistress have been made because of threshold exceedances, an affirmativeresult of test 37 in FIG. 8 will reach steps 40 in which a distress flagis set (indicating that the M portion of the record is complete); an NPTR (described hereinafter) is set equal to the current value of the RPTR; and the point where the next M records will be stored is marked bysetting BEG M equal to the R PTR. And then the program ends through thepoint 14.

Completing a Group of M & N Records

As described briefly hereinbefore, once a distress threshold number, M,of records (ten times the normal number of records which should occur ina healthy engine within a given alarm interval) has been collected, anadditional number, N, of records is collected to provide a completeclassification group consisting of M+N records. To achieve this, datasamples are continuously taken as described with respect to steps andtests 4-7 and compared against thresholds to determine if an exceedancerequires declaring another record, as described with respect to stepsand tests 8-11. When a record is declared, the related (26 prior and onecurrent history) samples in the history buffer are moved to anappropriate portion of the record buffer, and the remainder of therecord is taken on-the-fly as described with respect to steps and tests4-7, and 30-33, hereinbefore. The next time that a record is completedas indicated by an affirmative result of test 33, the steps 35 areperformed and test 36 is now affirmative since the distress flag was setin the steps 40 at the completion of the prior record, which was the Mthrecord for the present group. This causes steps 42 to be reached inwhich the number N is incremented and an N pointer is advanced. Sincethe R pointer is advanced in step 35 to be ready for the next record insequence and the N pointer is set equal to the R pointer in the steps40, the N pointer initially points to the first of the N subsequentrecords. The use of the N pointer keeps track of the advancing storageposition within the record buffer where the N records are being stored.

In FIG. 8, a test 43 determines if the current, Nth record is thedesired maximum number of N MAX records or not. If not, the routine ofFIG. 8 ends at point 14. But when the required number of subsequentrecords is reached, an affirmative result of test 43 reaches a series ofsteps 44 where N is reset to zero, the designation of the current group,G, is incremented, the beginning record for the current group isidentified as the beginning of the M portion of the group, asestablished either in the step 40 of FIG. 8 or in the step 16 of FIG. 7,as described hereinbefore. And the classification flag for group G isset meaning that group G has to be classified and has not yet been. Thedistress flag is reset so as to enable collecting a whole new group ofrecords, and distress may be indicated to a pilot or test apparatusoperator, as appropriate. Following the steps 44, the routine of FIG. 8ends at point 14. This leaves the apparatus in condition where it has agroup to be classified; however, sampling of the probes on a kilohertz(or so) rate, declaring records when any probe has a thresholdexceedance, collecting complete records until a distress thresholdnumber of them have been completed (within the given alarm interval) andadding an additional records thereto to provide a full classsificationgroup, will continue on a real time interrupt basis as described withrespect to FIG. 8 hereinbefore. Once a number of thresholds have beenexceeded and the corresponding number of records of triplets, containing104 samples each, for each of the three probes, have been made, the factthat a unit of distress has occurred (exceeding the distress thresholdin test 37, FIG. 8) is indicated by the distress flag.

Record Classification--FIG. 9

The record classification routine of FIG. 9 is reached on a periodicbasis in each pass through the major cycle of the computer, other thanduring interrupts (as described hereinbefore). Entry of the recordclassification routine through a point 1 in FIG. 9 reaches a test 2 todetermine if classification of the G' group of records is required. Ifnot, the program is ended through a point 3 without performing anyfurther steps in the record classification routine of FIG. 9.

Whenever distress has been indicated and a group (G) of records (M+N innumber) have been stored in the record buffer (as described with respectto FIG. 8), but the group (G') has not yet been classified, the recordclassification routine of FIG. 9 will see an affirmative result of test2, reaching a plurality of steps 3: the maximum sample is set equal tothe maximum sample in a given embodiment (which is established as 104samples in the present example): a group counter (which counts therecords within the current group as they are classified) is set equal tozero; and the record pointer (R' PTR) utilized in record classification(in distinction with that, R PTR, used for data acquisition, FIG. 8) isset to the beginning record of the group of distress records to beclassified (the beginning record set in steps 17 of FIG. 7, or in steps44 of FIG. 8), so that it will point to the first record of the group.This allows the accumulated records to be classified through the programof FIG. 9 interleaved with continuous acquisition of data in new recordsthrough the program of FIG. 8, on an ongoing basis, as shown in FIG. 2.

In FIG. 9, the iterative process begins in a series of steps 4 byadvancing the R' pointer and incrementing the R' counter and setting theprobe pointer, P', equal to the highest numbered probe, which in thepresent embodiment is three. Then a series of steps 5 advance the P'pointer (so that in the first pass it will point to probe 1), a samplebuffer is set equal to the record buffer for the current record andprobe (implying a data move of all 104 samples for one probe from therecord buffer to a sample buffer used during analysis), a samplecounter, S, is set to zero and a category counter, C, is set to zero.(The move of a record for a probe to the sample buffer is not requiredsince all the data may be accessed, when desired, from the recordbuffer. However, the description is much simpler when reference to R'and P' is not required for each sample.) Then in a step 6, the samplecounter is incremented to point to the first sample in the samplebuffer. Then a test 8 determines if the absolute value of the magnitudeof the first sample (a magnitude indicative of probe output voltage inthe present embodiment) exceeds the record threshold for that probe (ingeneral, the same threshold used in tests 9 and 10 and saved in steps 18of FIG. 8). If not, a test 10 in FIG. 9 determines if all 104 sampleshave been tested or not. If not, a negative result of test 10 returns tostep 6 to increment S and examine the next sample of the record for theparticular probe, for threshold exceedance. Assuming that the firstprobe in the record being examined did not have any signals exceedingits threshold (meaning the record was declared as a consequence ofactivity on one of the other probes), eventually test 10 will beaffirmative following 104 negative results of test 8. This will reach astep 11 where the category (the type of signal) for this probe withinthis record is set to zero, indicating that there is no record andtherefore nothing to be categorized for this probe within this record.Then a test 12 is reached to determine if the samples for all threeprobes have been interrogated in this record or not. If not, a negativeresult of test 12 will return to the series of steps 5 in which P' isadvanced and a new record of samples for the second probe is broughtinto the sample buffer from the record buffer, S and C are reset to zeroand then step 6 increments S so as to point to the first sample in therecord for the second probe. Depending upon whether there is any recordat all for this probe, or if this probe has a syntactic pulse shape oris a gross signal, a threshold may or may not be exceeded. If not, theprocess will repeat through step 11 as described hereinbefore. If thereis a threshold crossing as a result of one of the samples having amagnitude in excess of the record threshold for the particular probe,test 8 will eventually be affirmative leading to a step 13 where thesample at which threshold exceedance occurred is set equal to S, thecurrent sample number. Then a test 14 determines if this is the firstprobe being interrogated or not. If it is, an affirmative result of test14 will lead to a first probe routine 15 (described hereinafter withrespect to FIG. 10) which compares the sample record withcharacteristics of various categories of signals which can be sensed onthe first probe. If test 14 is negative, a test 16 will determine if thecurrent sample record being interrogated is for probe 2 or not. If itis, the routine will advance to a second probe routine 18 (describedhereinafter with respect to FIG. 11) which compares against the varioustypes of signals which can be sensed on the second probe. But if test 16is negative, then the routine of FIG. 9 advances to a third probesubroutine 20 (described hereinafter with respect to FIG. 12) whichcompares against the various types of signals which can be sensed on thethird probe. Regardless of which routine is used and dependent uponwhich probe is being analyzed, the program will advance from one of thesubroutines 15, 18 or 20, to a decision subroutine 21 (which isdescribed with respect to FIG. 13). In the decision subroutine 21, theresults of attempting to classify the given probe record into any one ofa number of categories is analyzed and one of the categories is picked(if possible).

In FIG. 9, when the sample buffer has been loaded for each of the threeprobes and the corresponding sample records analyzed, eventually test 12will be affirmative causing the program of FIG. 9 to reach a step 22 inwhich the group counter is incremented. Then a test 23 determines if thegroup counter has advanced to designate a full group of M+N records. Ifnot, a negative result of test 23 causes the program of FIG. 9 to returnto the series of steps 4 so as to advance the R' pointer, increment theR' counter and set P' equal to 3 so that the next record in theclassification group can be passed through the iterative part of theroutine of FIG. 9 to have the samples for each of the three probescategorized. When an entire group of records (such as thirty records orso), each having 104 samples for each of three probes, has beenclassified, test 23 will be affirmative causing the program of FIG. 9 toadvance to a step 24 in which the classification flag for the G' groupis reset. Then a test 25 determines that further distress analysisroutines are available in the present embodiment of the invention, asdetermined by a permanent distress-analysis-available flag and atemporary distress analysis flag is set in a step 26. In thisembodiment, test 25 is never negative, so G' is not incremented in astep 27 so as to point to the next group in the sequence. Then theprogram will finally end at the point 3. An example of distress analysisis described with respect to FIG. 81, hereinafter.

In subsequent calling of the record classification program of FIG. 9, ifall existing groups have been classified, test 2 of FIG. 9 will benegative causing the program to end at point 3. The utilization of theclassification flag for the G' groups permits classification to be doneasynchronously with acquisition of groups of records to be classified.Thus if the classification program falls behind the acquisition of newrecords (which is usually unlikely but might possibly happen during ahighly active engine condition), so long as the record buffer is notfull, data acquisition can continue.

First Probe Subroutine--FIG. 10

The first probe subroutine 15 of FIG. 9 is reached in FIG. 10 through anentry point 1 and a first step 2 sets C MAX for the first probe (P')equal to 6, since the present embodiment has provision to discriminatebetween six different categories which may be sensed by the first probe.Of course, this number can vary, in any given embodiment. The iterativeprocess of the first probe subroutine begins in FIG. 10 by a series ofsteps 3, the first of which increments the category counter, C, so as toadvance it from the zero setting of steps 5 in FIG. 9 to cause therecord set in the sample buffer in steps 5 of FIG. 9 to be examined forthe first category (C=1) of the first probe in the subroutine of FIG.10. Then a parameter buffer is loaded with the parameters shown inillustration (c) at the top of FIG. 6 for the first probe and the firstcategory, as set forth in Table 2. A quality factor, Q, (an indicationof how well a given sample record fits into a given category) is set tozeros, and a degrade factor (utilized in determining Q) is set to zeros.

In FIG. 10, a test 4 determines if the current category to test thesample against is the first category or not. Initially it is, so anaffirmative result of test 4 reaches a step 5 in which a sign is setequal to plus. This sign value defines the polarity (+or -) of theprimary, threshold-exceeding pulse of a pulsatile category; a recordwith an opposite pulse cannot be of that category. This can be achievedby having a sign value which is set to a positive integer in contrastwith being set to a negative integer, or in any other way as desired.Then a narrow pulse subroutine, described hereinafter with respect toFIG. 25, is called to determine if the current sample record isclassifiable as an initially positive-going, narrow pulse indicative ofmetal rubbing on an abradable seal in the compressor, as exemplified inFIG. 57, by utilizing the parameters set forth in Table 2 for probe 1,category 1, fetched in steps 3. After completion of the narrow pulsesubroutine 6, the quality factor Q determined in that subroutine isstored as the Q for category 1, in steps 7. If desired, and if suitablestorage capacity is available, all of the results of the processingwithin the narrow pulse subroutine 6 may be stored at this point in thesubroutine, if desired. Then a test 9 determines if the current categoryis the maximum category (6 for the first probe in the presentembodiment). If not, the subroutine of FIG. 10 returns to the steps 3 toset up operation for testing the sample against the second category. Thecategory counter, C, is incremented and new parameters are brought intothe parameter buffer as illustrated in Table 2 for probe 1, category 2.Then, test 4 is negative and a test 10 is affirmative so that a step 11sets the sign to a negative value and the narrow pulse subroutine 6 isagain called utilizing, the parameters for probe 1, category 2 todetermine if the sample record for probe 1 is classifiable as aninitially negative going, narrow pulse indicative of metal-to-metalrubbing in the compressor, as exemplified in FIG. 58.

The resulting quality factor is stored for the second category and test9 determines if all categories have been checked or not. In this case,they have not, so a negative result of test 9 reaches the steps 3 onemore time. C is incremented so that parameters illustrated in Table 4for probe 1, category 3 are loaded into the parameter buffer. Q anddegrade are reset to zeros and tests 4 and 10 are negative leading to atest 13 which will be affirmative. This reaches a surge subroutinedescribed with respect to FIG. 43, hereinafter, which processes thecurrent first probe sample record to see how closely it compares with acompressor surge record, an example of which is illustrated in FIG. 59.Then the quality factory Q is saved for the third category, results maybe stored if desired, and the subroutine of FIG. 10 continues in a likemanner for additional categories. Specifically, a test 15 determines acategory 4 should reach a loose electrode subroutine 16, described withrespect to FIG. 44 hereinafter, wherein the parameters of Table 5 areutilized to determine if the electrode within the first probe is looseas indicated by a signature exemplified in FIG. 60. And, finally, anegative result of test 15 will reach a loose probe/rub strip subroutine17, described with respect to FIG. 54 hereinafter, to determine if probe1 had a loose probe connector, as exemplified by the waveform of FIG.61, using the parameters of Table 6 for probe 1, category 5. Then Q forthe fifth category is set in steps 7; test 9 is negative, and C isincremented to 6 in steps 3. Again test 15 is negative, reaching thesubroutine 17, but this time to determine if a rub strip (compressorabradable seal) has peeled off, by means of parameters illustrated inTable 6 for probe 1, category 6. An exemplar of the signature of a rubstrip peeling off is illustrated in FIG. 62. When the sample record forthe first probe has been compared against all six categories of thepresent embodiment, the record classification program of FIG. 9 isreverted to through a return point 18. In FIG. 9, the decisionsubroutine 21 is reached, as described with respect to FIG. 13hereinafter, and the program then reverts to the steps 5 for the nextprobe in the sequence, eventually reaching the second probe subroutine18 as illustrated in FIG. 11.

Second Probe Subroutine--FIG. 11

In FIG. 11, the second probe subroutine is entered through a point 1 anda step 2 sets the maximum number of categories for the second probeequal to 8. These are the categories for which exemplary wave shapes areillustrated in FIG. 60-FIG. 67, respectively. The iterative part of thesecond probe routine of FIG. 11 is similar to that described for thefirst probe with respect to FIG. 10. Specifically, the steps 3 and 4 arethe same but for the second probe, tests 5 and 6 call a wide pulsesubroutine 7, described with respect to FIG. 34 hereinafter, after astep 8 sets the sign negative; a test 10 causes setting of a positivesign in a step 11 before calling the wide pulse subroutine 7. Then tests12 and 13 cause categories 4 and 5 to be examined with plus and minussigns, as set in steps 14 and 15, by means of the narrow pulsesubroutine 16. Test 17 causes the record to be examined in the looseelectrode subroutine and causes the record to be compared againstcategory 7 and then category 8, in the loose probe/rub strip subroutine19. When the sample record has been compared against all eightcategories, a test 20 causes the record classification program of FIG. 9to be reverted to through a return point 21.

In FIG. 9, the decision subroutine 21 is performed with the Q valuescollected by the second probe subroutine of FIG. 11 and then the thirdprobe is handled by negative results of tests 14 and 16 in FFF. 9reaching the third probe routine 20 of FIG. 12.

Third Probe Subroutine--FIG. 12

In FIG. 12, the third probe routine is reached through a point 1 and astep 2 sets the maximum number of categories equal to 14. In theiterative part of the program, the steps 3 are performed in the samefashion as in FIGS. 10 and 11 but fetch the parameters for the thirdprobe categories. As in FIG. 10 and FIG. 11, a series of tests 4-16cause the routine to examine the sample record for the third probeagainst 14 catgories, exemplary wave shapes for which are illustrated inFIG. 62 and in FIG. 68-FIG. 80 hereinafter. A series of steps 19-24 setthe sign as appropriate and, depending upon the particular category, thesample record is examined for its likelihood of being in that categoryby the narrow pulse, wide pulse, and loose connector/rub stripsubroutines 26-28 in the case of categories 1-3, 4-9 and 10,respectively. The sample record is examined for categories 11 and 12 byan abnormal A/B chop subroutine 30, described with respect to FIG. 54hereinafter, for category 13 in a normal afterburner chop subroutine 31,described with respect to FIG. 55 hereinafter, and for category 14 in anacceleration/deceleration subroutine 32, described with respect to FIG.56, hereinafter. In each pass through the routine of FIG. 12, the steps33 are the same as steps 7 in FIG. 10 hereinbefore, except relating tothe third probe, and when the record has been compared against allcategories, a test 34 causes the record classification program of FIG. 9to be reverted to through a return point 35.

In FIG. 9, the decision subroutine 21 is called with respect to thethird probe, which completes the examination of all three probes for onegiven record, as described with respect to FIG. 9 hereinbefore.

Of course, if new categories are found to be useful for any probe, newsubroutines and expansion of each probe subroutine can be made, asdesired.

Decision Subroutine--FIG. 13

In each of the subroutines called by the first probe, second probe, andthird probe subroutines of FIG. 10-FIG. 12, the relative likelihood thatthe given sample record fits into the category related to the particularsubroutine is manifested by the quality factor, Q. The manner in whichthis quality factor is developed, for each sample record as it isprocessed through each subroutine, is described with respect to FIG. 24through FIG. 56 hereinafter. In the present embodiment, the qualityfactors generally range from zero to one, although this may differ independence on the manner in which the present invention is implemented.For the purposes of describing the decision subroutine illustrated inFIG. 13, it suffices to say that quality factors, Q, are assigned foreach sample record of each probe with repect to each of the categorieswhich may relate to that probe, and these quality factors range fromzero to unity. Following each of the individual probe subroutines 15,18, 20 of FIG. 9, the record classification program calls the decisionsubroutine 21, illustrated in FIG. 13. In FIG. 13, the decisionsubroutine is entered through a point 1 and a series of steps 2 set atemporary value, Q MAX, equal to zero; set the category equal to zero;and set the category counter, C, equal to zero. Then a first iterativepart of the subroutine of FIG. 13 commences with a step 3 whichincrements C and a test 4 determines if the quality factor assigned tocategory C is less than or equal to the maximum quality factor. For thefirst category in the set of categories for any given probe, test 4 mustbe negative since Q MAX is set at zero in the steps 2. Thus Q MAXbecomes set in one of the steps 5 to the Q for the current category andthe category for the probe is set equal to C. That is to say, thewinning category is set to be equal to the category (identified by C)for which Q MAX is most recently set equal to Q of the current category.Then a test 6 determines if C MAX (as set in step 2 of FIG. 10, FIG. 11or FIG. 12) has been reached or not. If not, this means all of thecategories for the given probe have not had their Q values examinedagainst the others as yet, and a negative result of test 6 will causethe decision subroutine of FIG. 13 to revert to step 3, where C isincremented to identify the next category in the sequence. If itsquality factor is not equal to or less than the previously determinedmaximum, its value is taken as the maximum and it is identified as thecategory for that probe in the steps 5. When all of the categories forthe given probe have been examined, an affirmative result of test 6 willreach a test 7 in which Q MAX is compared against some threshold valuefor Q which may be established. For instance, the Q threshold may be setat 0.5, in the general case of the present exemplary embodiment. If agiven category has too low a Q value, an affirmative result of test 7will reach a step 8 in which the category for the record under test forthe current probe is set equal to the maximum category number plus 1,which is used to define the record as of "unknown" characteristics. Thusfor the first probe, if Q MAX is zero (meaning the particular samplerecord does not in any way resemble any of the six permitted categoriesfor the first probe), or if the maximum Q is less than 0.5, the categoryfor this sample record for this probe will be set (in step 8) to seven,meaning the category is unknown. On the other hand, if the highest Qvalue for the given sample record for the particular probe is equal toor greater than 0.5, a negative result of test 7 will reach steps 9 inwhich the quality factor, for the particular record involved and for theparticular probe involved, is set equal to the Q MAX provided in thesteps 5. And the category for the particular record and particular probeis set equal to the category determined in the steps 5. Following eithersteps 8 or 9, the classification program of FIG. 9 is reverted tothrough a return point 10 in FIG. 13.

Basic Subroutines--FIG. 15-FIG. 24

Each of the subroutines referred to in FIG. 10 through FIG. 12 whichdetermine the likelihood that the record represents a wave shapeindicative of a given category, utilize one or more basic (primitive orroot) subroutines of FIG. 15-FIG. 24, an understanding of which isnecessary as a precursor to the understanding of the subroutines of FIG.25-FIG. 56. Each of these basic subroutines operate on the magnitude ofthe individual samples related to the given probe involved within thesample buffer record which is brought into the record classificationprogram by steps 5 in FIG. 9. In these subroutines, S refers to thesample number (of the 104 samples in the given example) and V relates tothe voltage, the value, or the magnitude of a given sample (which forthe purposes of describing these subroutines can be taken to be the samething). Further, in the case where no record has been sensed for a givenprobe, no classification is made of that record, the category beingforced to zero (step 11, FIG. 9). Thus, all of the classificationsubroutines described herein are only called when there was a thresholdcrossing within the record and therefore some threshold-exceedingactivity which can be compared in the subroutines.

Width/Peak--FIG. 14

Referring now to FIG. 14, a width/peak subroutine finds the width of aprimary pulse of those categories which are pulse-like in nature, anddetermines the sample number and magnitude of the peak of the primarypulse. If a width A.G.C. request is made prior to calling thesubroutine, the subroutine is performed a first time just to find thevalue of the primary pulse peak, and then a second time utilizing awidth threshold which is a function of the magnitude of the peak foundduring the first execution of the subroutine.

In FIG. 14, the width/peak subroutine is reached through an entry point1 and a series of steps 2 reset an A.G.C. once flag (which keeps trackof when the second iteration has been made as a function of the peakmagnitude, if used); the sample number of the peak is arbitrarily presetas the beginning sample (the number of the sample which crossed theprobe threshold within the record under consideration); the value of thepeak is arbitrarily set to equal that of the beginning sample; and alocal sign value (SIN) is set positive. The local sign value is used soas not to overwrite the sign value set by one of the calling subroutinesof FIG. 10-FIG. 12, which must be retained as indicative of the polaritywhich the primary pulse (that which caused the threshold crossing), musthave for such category, as becomes more apparent in the description ofother subroutines hereinafter.

In FIG. 14, a test 3 determines if the beginning sample is negative, andif so, an affirmative result reaches a step 4 in which the local sign isset negative. If the begining sample is not negative, step 4 isbypassed. Then a step 6 sets a sample counter equal to the beginingsample (the sample which the subroutine has been commanded to beginwith). A test 7 determines if the value of the beginning sample isgreater in magnitude than the value of the heretofore arbitrarily setpeak, in either the positive or the negative direction. That is, if thecurrent sample is more negative than a previously established negativepeak, test 7 will be affirmative; if the current sample is more positivethan a positive peak, test 7 will be affirmative. If test 7 is positive,the new sample indicative of peak is set equal to the current sample,and the value of the peak is set equal to the value of the currentsample, in steps 8. If test 7 is affirmative, steps 8 are bypassed.

Then, a test 10 determines if the value of the current sample is lessthan a threshold magnitude at which width is to be determined; bymultiplying with the sign, positive sample values are retained positiveand negative sample values are converted to positive, so that onlypositive thresholds need be used in the test 10. In the general case,the width threshold is quite low compared to the probe threshold whichwould recognize a pulse (such as compressor metal-on-metal rubbing,probe 1, category 2, FIG. 58, and the like). Therefore, in the initialfew samples tested, test 10 is likely to be negative thereby reaching atest 12 wherein it is determined whether or not the sample is the firstsample of a record (sample 1). Initially, such will not be the case anda negative result of test 12 will reach a step 13 which decrements S andreverts to test 7. In this manner, the steps and tests 7-13 begin at apoint usually approximately equal to the 27th sample, (as set in step 13of FIG. 9), stepping downwardly to the beginning of the record andlooking to see if there are any peaks higher than the point of thresholdcrossing. In other cases, the width/peak subroutine may be called toexamine the width of a following pulse; in such cases, the beginningsample is set at the sample which had been determined to have the peakvalue for the following pulse so that a similar situation exists:starting at the peak of the pulse and working downward through lowersample numbers, the steps and tests 7-13 look for any higher peak andfor a crossing in the value below a width threshold.

In FIG. 14, in the event that the value of a given sample is less thanthe width threshold, an affirmative result of test 10 will cause atemporary beginning sample number, S(BEG), to be set equal to thecurrent sample number. But if there is no affirmative result of test 10,starting with the beginning sample and ending up with the first,leftmost sample in the record, a negative result of test 10 followed byan affirmative result of test 12 will reach a step 15 in which thetemporary beginning sample number is set equal to zero.

In FIG. 14, following steps 14 or 15, a similar process is repeated butstarting just ahead of the beginning sample and working upwardly (to theright) to see if there are and peaks of a magnitude greater than thebeginning sample and to determine when the pulse drops below thethreshold value at the upper sample end thereof. Specifically, a step 17sets the current sample number equal to one greater than the beginningsample. Then a test 18 determines if the value of the current sample isgreater than the value of the previously determined highest valued(peak) sample, which may have been established in steps 8 or by thepreset of steps 2. If the current value is higher, an affirmative resultof test 18 will reach steps 19 to set the sample number for the peakequal to the current sample number and to set the value of the peakequal to the value of the current sample. But if the current sample doesnot exceed the previously established peak, a negative result of test 18will bypass the steps 19. Then a test 20 determines if the upper end(higher sample number end) of the pulse has decreased below the widththreshold value or not. If not, a negative result of test 20 reaches atest 22 which determines if the current sample number is equal to themaximum sample number of the record (sample number 104, in the exampleherein), or not. If not, the sample number is incremented in a step 23and the steps and tests 18-20 are repeated again. When the value of thecurrent sample decreases below threshold, an affirmative result of test20 will reach a step 24 which causes a temporary end-of-pulse samplenumber, S(END), to be set equal to the current sample number. But if themaximum sample number is reached without ever decreasing below thethreshold value, a negative result of test 20 followed by an affirmativeresult of test 22 will cause a step 26 to set the temporary end-of-pulsesample number to be set equal to one greater than the maximum sample(for purposes described hereinafter).

In FIG. 14, following steps 24 or 25, a test 27 determines if widthA.G.C. had been commanded by the calling subroutine, which is the casewhen called by the narrow pulse subroutine and wide pulse subroutinewith respect to the primary pulse of a record. If so, an affirmativeresult of test 27 reaches a test 28 to determine if the second passthrough the width/peak subroutine has been accomplished for the purposesof examining width with a varied threshold, or not. If it has, an A.G.C.once flag will have been set, and an affirmative result of test 28 willcause bypasing of any further iterations through the subroutine of FIG.14. On the first pass through, however, the test 28 is negative becausethe flag is reset in the steps 2. This reaches steps 30 in which thewidth threshold is used as a fraction to find the desired widththreshold by multiplying it by the absolute value of the peak magnitudefound for the pulse during the first pass through the subroutine. IfA.G.C. is invoked, the initial value of THRSH is set in the callingprogram to be a decimal fraction (0.0 to 1.0) of the peak value foundduring the first pass through the subroutine. Step 30 then computes theabsolute threshold by multiplying the percent-threshold by the peakvalue. In this mode of operation, the initial THRSH value is notcritical (any low positive value will suffice) because the first pass isused solely to get V(PK), and not to get the exact width.

In FIG. 14, when the A.G.C. has been set up by steps 30, the steps andtests 6-25 are repeated, with the adjusted width threshold. The stepsand tests 7, 8 and 18, 19 will be unproductive, since the highest peakhas already been found and the change in threshold does not vary that atall. Thus, the iterative processes are to look to the left to find theleft-most threshold by test 10 and to look to the right to find theright-most threshold by test 20.

When the second pass through the iterative processes of FIG. 14 iscompleted, if the width A.G.C. had been commanded, test 27 is againaffirmative but test 28 is affirmative so that the subroutine advancesto steps 32 to define the beginning sample of the pulse as that samplenumber which just falls below the threshold, by causing the beginningsample to be equal to S(BEG) as set in step 14 and set the end sample tobe equal to the sample having a value just above the width threshold, bycausing it to be set to equal one sample less than S(END) set in step24. On the other hand, if thresholds were not crossed, the beginningsample will equal zero and the ending sample will equal the maximumsample, due to the combination of steps 15, 25 and 32. And, the width isthen set equal to the difference between the end sample and thebeginning sample. Then the program returns to the routine which calledthe width/peak subroutine of FIG. 14, through a return point 33.

Following-Peak Subroutine--FIG. 15

The following-peak subroutine of FIG. 15 is utilized to find thelocation, S(PK) and the magnitude, V(PK), of the first peak exceeding afollowing-peak threshold in a sample interval extending from a beginningsample to an ending sample that is defined to the subroutine by theroutine which calls it. If the absolute maximum peak of a followingpulse is desired, the width/peak subroutine is called thereafter forthat purpose. The subroutine can search leftward from high samplenumbers to low sample numbers (reverse) or it can search rightward fromlow sample numbers to high sample numbers (forward). And, in eithersearching direction, the subroutine can be caused to look for justpositive peaks, just negative peaks, or either, in dependence uponwhether a sense command is set equal to +1, -1, or zero, respectively.

In FIG. 15, the following-peak subroutine is reached through an entrypoint 1 and the sample number and value of the peak are preset to zeroin steps 2. If the calling program desires finding the first peak in aleftward or reverse search, it provides a reverse command to thesubroutine of FIG. 15, which is sampled in a test 3. First, assumingthat the reverse command has not been made, test 3 will be negative so astep 4 will set the sample counter S to the beginning sample, which mayeither be the first sample of the record in some cases or it may be thesample to the left of a pulse in other cases. The routine proceedsiteratively, simultaneously looking for both a negative peak and apositive peak. S is incremented in a step 5 and the value of S iscompared with the value of the next lower sample in a test 6 to see ifit is more positive than the next lower numbered sample. If it is, thismeans the next lower numbered sample is the first negative peak in thedirection of scan, as in FIG. 16. An affirmative result of test 6reaches a test 7 which determines if this negative peak value is atleast as negative as a minus following-peak threshold. If it is not, thevalue of the next lower sample number is not accepted as a peak, as inFIG. 17. But if it is as negative as the minus following-peak threshold(FIG. 16), a negative result of test 7 reaches a test 8 to determine ifnegative peaks are of interest to the call program. In test 8, the sensecommand may be either -1, 0 or +1. If it is -1 or 0, then negative peaksare of interest to the calling program and the sense command is equal toor less than zero, so that an affirmative result of test 8 will reachsteps 10 in which the sample number of the peak is taken to be equal toone less than the current sample number and the value of the peak is setequal to the value thereof.

In FIG. 15, if either test 6 or 7 is negative, this means that anegative peak has not been identified by comparing the value of thecurrent sample number with the value of the next lower sample number. Orif test 8 is negative, that means that only positive peaks are beinglooked for and a negative peak should be ignored (if found). In any ofthese situations, a test 12 determines if the value of the currentsample number is less positive than the value of the next lower samplenumber. If it is, an affirmative result of test 12 reaches a test 13 todetermine if the value of the next lower sample is more positive than apositive following peak threshold. If it is, this means that a positivepeak of a sufficient magnitude has been located, as in FIG. 18. Anaffirmative result of both tests 12 and 13 reaches a test 14 whichdetermines if positive peaks are being looked for. This is the casewhenever the sense command is set at either zero or +1. If such is thecase, an affirmative result of test 14 will reach the steps 10 toidentify the sample number of the peak and its value as being those ofthe next lower sample.

In each iteration (for subsequent values of S) of the subroutine of FIG.15, if a negative peak is not found, or when found is not desired,negative results of tests 6-8 will reach tests 12-14. If a positive peakis not found or is not desired, negative results of tests 12-14 willreach a test 18 to determine if the end sample defined by the callingprogram has been reached or not. The end sample may typically be themaximum sample (104 in the present example), but it need not be. If theend sample has not been reached, a negative result of test 18 causes theprogram to revert to step 5 where the S counter is incremented and thepresent sample is compared with the preceeding sample in the tests 6and/or 12. A feature of the subroutine of FIG. 15 is utilizing the senseword to define whether a negative peak is being looked for, or apositive peak is being looked for, or any peak, whether positive ornegative is being looked for. This permits examining wave shapes foropposing or non-opposing following peaks, in a simple manner.

When the forward portion of the subroutine of FIG. 15 has beencompleted, either by reaching the end sample or by finding a peak of adesired polarity, completion of steps 10 or a negative result of test 18will cause the program to revert to the calling routine through a returnpoint 20.

In FIG. 15, if the calling program desired to find the first peak to theleft of some point, it will set the reverse flag and an affirmativeresult of test 3 will reach a step 22 where the sample counter is setequal to the end sample (the left-most sample) defined by the callingroutine, to commence scanning in the reverse direction. Then a series oftests 23-25 look for a desired negative peak in the same fashion astests 6-8. If a desired negative peak is found, steps 27 identify thesample and the value of the peak as those of the next higher numberedsample. On the other hand, if a negative peak of sufficient magnitude isnot found or a negative peak is not desired, negative results of any oftests 24-26 will reach a series of tests 29-30 looking for a desiredpositive peak, as in FIG. 19. If one is found, steps 27 identify thesample and value of the peak. Normally, the first few samples will notindicate having crossed a peak, and negative results of tests 24 and 29will reach a test 34 to determine if the beginning sample (wherescanning is to end in the reverse scan case) has been reached or not.Notice in FIG. 19 that the following-peak threshold can be set to avalue which will cause small peaks of no interest to be ignored; only apeak of interest is thus identified. If not, a negative result of test34 reaches the step 23 and the process repeats until a peak has beenfound. An affirmative result of test 34, indicating that all the sampleshave been tested and no peak found, or passage through steps 27 whichidentify a peak, will cause the program to revert to the calling routinethrough the return point 20.

Multiple Peaks Subroutine--FIG. 21

Referring to FIG. 21, a multiple peaks subroutine is reached through anentry point 1. The multiple peaks subroutine is utilized specifically tosense closely adjacent positive peaks of the same polarity, as occurswhen there is an impact induced turbine rub, of the type illustrated inFIG. 74. However, the multiple peaks subroutine of FIG. 21 can detectany number of adjacent positive peaks. In a series of steps 2, an extrapeaks value (a value indicative of how many peaks are found by thesubroutine) is preset to zero; a valley flag used in the subroutine isreset; and the S counter is set equal to the beginning sample, which isidentified by the calling program. The iterative part of the subroutineof FIG. 21 begins with a test 3 which determines if the value of thecurrent sample is equal to or greater than a multiple peak highthreshold which is provided to the subroutine by the calling program, asshown in FIG. 20. The multiple peak high threshold is a threshold valuewhich a peak must exceed in order to be recognized as such. Since thebeginning sample is normally set as the start of a wide pulse of somesort, the first few passes through the test 3 are likely to be negative,in the general case. This reaches a step 4 where S is incremented and atest 5 which determines if S is set to the end sample (normallyidentified as the end of a wide pulse). If test 5 is negative, the nextsample is tested to see if its value exceeds the multiple peak highthreshold. This will continue until finally the value of the currentsample does exceed the multiple peak high threshold, which causes anaffirmative result of test 3. This reaches a test 7 which interrogatesthe valley flag; the first pass through test 7 is always negativebecause the valley flag is reset in the steps 2. Resetting of the valleyflag is reinforced in step 8 and a test 9 determines if the currentvalue is below a multiple peak low threshold. This is a threshold valuethat the pulse wave shape must dip down under to recognize theseparation between the first peak and a subsequent peak. Initially, thefirst pass through test 9 has to be negative since the same samplecannot both be higher than the multiple peak high threshold and lowerthan the multiple peak low threshold. Thus an ensured negative result oftest 9 will reach a step 10 which increments S and a test 11 which testsS to see if the end sample has been reached yet, or not. In the generalcase, it has not, so the next sample is tested in test 9 to see if itsvalue is below the multiple peak low threshold. This process continuesuntil the sample value dips below the multiple peak low threshold whichcauses an affirmative result of test 9 to reach a step 12 which sets thevalley flag (see FIG. 20). Then the program returns to step 3 to lookfor the next subsequent peak. Initially, when the test 9 is affirmative,test 3 has to be negative because the sample cannot have a value whichis both below the low threshold and above the high threshold. Therefore,a negative result of test 3 will again reach step 4 to increment S andtest 5 to see if the end sample has been reached or not. This processrepeats until once again the value of the sample exceeds the multiplepeak high threshold (if there is an additional sample which will do so).When a second or subsequent peak is sensed, an affirmative result oftest 3 finds step 7 affirmative and therefore reaches a step 14 whichincrements an extra peaks counter, thereby keeping track of how manypeaks in excess of one have been sensed by the subroutine of FIG. 18.After sensing each peak through test 3, the routine reaches test 9 andlooks for a following valley, sets the valley flag, and looks for asubsequent peak until the end sample is reached. This subroutine may bemodified to look for multiple negative peaks, in an obvious manner. Anaffirmative result of either tests 5 or 11 will cause the callingroutine to be reverted to through a return point 15.

Zero Crossings Subroutine--FIG. 22

Referring now to FIG. 22, a zero crossings subroutine is reached throughan entry point 1. This subroutine senses the number of times that thevalue of the samples changes from positive to negative, or vice versa,concurrently with the respective magnitudes of the two samplesexhibiting the polarity change differing by some threshold amount. Thisthreshold amount determines the degree of immunity to ordinary noise. InFIG. 22, a pair of steps 2 preset the number of zero crossings (which isthe value that the subroutine of FIG. 22 determines) to zero, and the Scounter is set equal to the beginning sample specified by the callingroutine. In the iterative portion of FIG. 22, a series of steps 3increment S and then take the product of the value of the current sampleand the value of the preceding sample. If the two samples are bothnegative or both positive, the product will be positive. But if they areof opposite sign, the product will be negative. And, the difference istaken as the absolute value of the difference between the current samplevalue and the value of the next lower numbered sample. Then a test 4determines if the product is positive. If it is, this means that the twosamples are of the same sign and there has not been a zero crossing. Anaffirmative result of test 4 reaches a test 6 to determine if the endsample, as defined by the calling program has been reached. If not, thesubroutine of FIG. 22 reverts to the steps 3 to compare the next pair ofsamples.

If a zero crossing has occurred, test 4 will be negative reaching a test7 which determines if the difference is equal to or greater than azero-crossing threshold, and thereby to be recognized as a zero crossing(rather than merely noise). If so, an affirmative result of test 7 willreach a step 8 wherein the number of zero crossings is incremented.Otherwise, step 8 is bypassed. When the end sample has been reached, anaffirmative result of test 6 causes the program to revert to the callingsubroutine through a return point 9. The number of zero crossings thusdetermined is indicative of frequency content of a gross signal, and canreadily discriminate between relatively low frequency signals, such asthat exemplified in FIG. 61, from relatively high frequency signals,such as that exemplified in FIG. 62. This provides a course indicationof frequency content without the heavy computational burden required forother methods, such as the fast Fourier transform.

R.M.S. Subroutine--FIG. 23

In FIG. 23, an R.M.S. subroutine is reached through an entry point 1 anda pair of steps 2 preset the intial R.M.S. value to zero and set the Scounter to the beginning sample identified to the subroutine by thecalling program. Then a step 3 adds to the R.M.S. value the square ofthe sample value. A test 4 determines if the end sample defined by thecalling routine has been reached or not, and if not, a step 5 incrementsS and returns to step 3. When the end sample is reached, the R.M.S.value is set in a step 6 to be equal to the square root of the R.M.S.value divided by the sample interval. The interval includes the endsample minus the beginning sample, plus one, to account for thebeginning sample. Then the calling program is reverted to through areturn point 7.

Degrade Subroutine--FIG. 24

In FIG. 24, a degrade subroutine is reached through an entry point 1 anda pair of steps 2 determine the variation in a measured parameter from anominal value for that parameter, related to a given category againstwhich a sample record is being compared. For instance, the measuredvalue may be a pulse width which is compared against a nominal pulsewidth for the given category. Comparison of the exemplary wave shapesshown in FIG. 73 and 74 illustrates that pulse width can be a gooddiscriminant between some categories, although it may not be withrespect to others. In any event, in the steps 2, an increment is setequal to the ratio of the variation to the sensitivity raised to adegradation exponent. The exponent determines how nonlinearly thedegradation value will increase as the variation increases. Forinstance, an exponent greater than unity will weight large variationsmore heavily than small variations. For example, for exponent=2 andvariation=1, the net degradation is 1² =1; but for variation=2, the netdegradation is 2² =4: a fourfold increase in degradation. The incrementis truncated by having any decimal fractions stripped off. Thesensitivity is in a sense an indication of a range of variation which istolerable. Thus, if the variation is less than the sensitivity, theincrement will be a fraction and the truncation will cause the incrementto become zero. Thus there is no degradation as a consequence of somemeasured value varying from a nominal value within the tolerance range.But the sensitivity factor is also a granularity factor because of thetruncation. Thus five-thirds (equaling about 1.66) is truncated to 1.0.If the initial variation were 3, 4 or 5 compared to a sensitivity of 3,the increment is truncated to 1. But if the variation is 6, 7 or 8 inthis example, the increment is truncated to 2, etc. Thus, the rate ofgrowth of increment per unit of variation (the incremental slope) iscontrolled by the sensitivity. The truncation of the increment alsoprevents there being any fractional increments. The final one of thesteps 2 updates the degradation factor, "DEGRADE", by adding theincrement to it. And then the calling routine is reverted to through areturn point 3.

Narrow Pulse Subroutine--FIG. 25

The narrow pulse subroutine is set forth in FIG. 25a-FIG. 25c. Theroutine is entered in FIG. 25a through an entry point 1 and a first step2 determines whether or not the sign is correct. It does this bymultiplying the value of the threshold sample (established in step 13 ofthe record classification program of FIG. 9) by the sign of the primarypulse of the category which is being examined for. The sign is set inany of: steps 5 or 11 in FIG. 10; steps 14 or 15 in FIG. 11; or steps 19or 20 in FIG. 12. If the primary pulse is of the correct polarity, theproduct will be positive. If it is not, a negative result of test 2 willcause the calling routine to be reverted to through the return point 2a,eliminating the current category from contention for this sample record.

                  TABLE 2                                                         ______________________________________                                        NARROW PULSE SUBROUTINE                                                                 PROB 1  PROB 2    PROB 3                                            PARAMETERS  C1     C2     C4   C5   C1   C2   C3                              ______________________________________                                        DEGRADE MAX 11     18     11   18   11   11   11                              FOLWNG PULS 2      2      2    4    2    2    5                               DVSR                                                                          FOLWNG PULS 0      2      0    4    0    1    10                              NOMNL WIDTH                                                                   FOLWNG PULS 9      10     6    8    8    8    10                              WIDTH LIM                                                                     OPOS PULS   0      3      0    5    0    0    5                               ABSNT                                                                         OPOS SEP LO 3      3      3    3    3    3    3                               LIM                                                                           PEAK THRSH  1      1      1    1    1    1    1                               PRE R.M.S.  .1     .2     .15  1.04 .15  .15  .1                              DVSR                                                                          PRIM PULS   2      2      1    2    1    1    3                               DVSR                                                                          PRIM PULS   2      4      3    3    2    3    3                               NOMNL WIDTH                                                                   PRIM PULS   8      10     6    8    8    8    10                              WIDTH LIM                                                                     POST R.M.S. .1     .3     .15  1.06 .15  .15  1.05                            DVSR                                                                          POST R.M.S. MAX                                                                           26     26     26   26   26   26   26                              INTVL                                                                         R.M.S. EXP  1      1      1    1    1    1    1                               SAME SEP LO 10     13     13   13   7    13   13                              LIM                                                                           SEPRATN DVSR                                                                              4      4      4    4    4    4    4                               SEPRATN EXP 1      1      1    1    1    1    1                               SEPRATN HI LIM                                                                            26     26     26   26   26   26   26                              WIDTH EXP   1      1      1    1    1    1.5  1                               WIDTH THRSH .05    .05    .08  .08  .05  .03  .03                             ______________________________________                                    

                                      TABLE 3                                     __________________________________________________________________________    WIDE PULSE SUBROUTINE                                                                    PROB 2   PROB 3                                                    PARAMETERS C1 C2 C3 C4 C5 C6 C7 C8 C9                                         __________________________________________________________________________    DEGRADE MAX                                                                              20 20 20 20 20 20 20 20 20                                         FOLWNG PULS                                                                              0  0  0  0  3  4  4  0  0                                          DVSR                                                                          FOLWING PULS                                                                             -1 -1 -1 -1 20 40 40 -1 -1                                         NOMNL WIDTH                                                                   MULT PK HI .8 .8 .8 .8 .8 .8 .8 .8 .8                                         THRSH                                                                         MULT PK LO .3 .3 .3 .3 .3 .3 .3 .3 .3                                         THRSH                                                                         OPOS PULS ABSNT                                                                          0  0  0  0  15 15 15 0  0                                          OPOS PULS PRSNT                                                                          5  5  5  7  0  0  0  5  5                                          PEAK THRSH 1  1  1  1  .6 .6 .6 1  1                                          POST R.M.S.                                                                              26 26 26 26 26 26 26 26 26                                         MAX INTVL                                                                     PRIM PULS DVSR                                                                           4  1  1  3  2  3  3  3  2                                          PRIM PULS  32 13 13 20 10 20 20 40 20                                         NOMNL WIDTH                                                                   PRIM PULS UPPER                                                                          0  0  0  6  0  0  0  0  0                                          WIDTH LIM                                                                     R.M.S. DVSR                                                                              .06                                                                              .06                                                                              .06                                                                              .05                                                                              .06                                                                              .06                                                                              .06                                                                              .04                                                                              .05                                        R.M.S. EXP 1  1  1  1  1  1  1  1  1                                          SEPRATN DVSR                                                                             5  5  5  5  5  5  5  5  5                                          SEPRATN EXP                                                                              2  2  2  2  2  2  2  2  2                                          SEPRATN HI LIM                                                                           26 26 26 26 26 26 26 26 26                                         SEPRATN LO LIM                                                                           7  4  4  7  5  5  5  7  7                                          TOTL DVSR  0  0  0  0  0  0  0  0  0                                          TOTL EXP   0  0  0  0  0  0  0  0  0                                          TOTAL PULS -1 -1 -1 -1 -1 -1 -1 -1 -1                                         NOMNL WIDTH                                                                   UPPER WIDTH                                                                              .6 .6 .6 .6 .6 .6 .6 .6 .6                                         THRSH                                                                         WIDTH EXP  1.5                                                                              1  1  1  1  1  1  1  1                                          WIDTH THRSH                                                                              .05                                                                              .05                                                                              .05                                                                              .05                                                                              .1 .06                                                                              .06                                                                              .1 .05                                        XTRA PKS DESIRD                                                                          0  0  0  0  0  0  1  0  0                                          __________________________________________________________________________

                  TABLE 4                                                         ______________________________________                                        SURGE SUBROUTINE                                                              PARAMETERS        PROB 1, C3                                                  ______________________________________                                        DEGRADE MAX       10                                                          ZERO CROS DVSR    1.5                                                         ZERO CROS EXP     1                                                           ZERO CROS LO LIM  2                                                           ZERO CROS NOMNL   8                                                           ZERO CROS THRSH   4                                                           ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        LOOSE ELECTRODE SUBROUTINE                                                    PARAMETERS        PROB 1, C4                                                  ______________________________________                                        DEGRADE MAX       6                                                           FOLWNG PK THRSH   1                                                           WIDTH LO LIM      26                                                          WIDTH THRSH       .08                                                         ZERO CROS DVSR    2                                                           ZERO CROS EXP     1                                                           ZERO CROS HI LIM  10                                                          ZERO CROS NOMNL   2                                                           ZERO CROS THRSH   .1                                                          ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        LOOSE PROBE/RUB STRIP SUBROUTINE                                                          PROB 1   PROB 2      PROB 3                                       PARAMETERS    C5      C6     C8     C7   C10                                  ______________________________________                                        DEGRADE MAX   13      13     13     13   13                                   R.M.S. DVSR   .15     .1     .1     .15  .1                                   R.M.S. EXP    1       1      1      1    1                                    R.M.S. LO LIM .5      .3     .3     .5   .3                                   R.M.S. NOMNL  .1      .5     .5     .1   .5                                   ZERO CROS DVSR                                                                              2       4      4      2    4                                    ZERO CROS EXP 1       1      1      1    1                                    ZERO CROS HI LIM                                                                            35      99     99     35   99                                   ZERO CROS LO LIM                                                                            8       21     21     8    21                                   ZERO CROS NOMNL                                                                             21      45     45     21   60                                   ZERO CROS THRSH                                                                             .3      .3     .3     .3   .3                                   ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        ABNORMAL A/B CHOP SUBROUTINE                                                                     PROB 3                                                     PARAMETERS         C11; C12                                                   ______________________________________                                        DEGRADE MAX        12                                                         HI NOISE LIM       15                                                         HI NOISE NOMNL     30                                                         HI NOISE THRSH     1.06                                                       LO NOISE INTVL LIM 22                                                         LO NOISE NOMNL     5                                                          LO NOISE LIM       10                                                         LO NOISE THRSH     1.12                                                       PEAK THRSH         .8                                                         R.M.S. DVSR        .1                                                         R.M.S. EXP         .1                                                         R.M.S. NOMNL       .6                                                         R.M.S. LO LIM      .3                                                         ZERO CROS DVSR     2                                                          ZERO CROS EXP      1                                                          ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        NORMAL A/B CHOP SUBROUTINE                                                                       PROB 3                                                     PARAMETERS         C13                                                        ______________________________________                                        DEGRADE MAX        15                                                         LO WIDTH DVSR      5                                                          LO WIDTH EXP       1                                                          LO WIDTH LIM       8                                                          LO WIDTH NOMNL     25                                                         LO WIDTH THRSH     .1                                                         PEAK THRSH         .5                                                         POST INTVL LO LIM  26                                                         R.M.S. DVSR        .07                                                        R.M.S. EXP         1                                                          R.M.S. HI LIM      .3                                                         R.M.S. NOMNL       0                                                          UPPER WIDTH DVSR   2                                                          UPPER WIDTH EXP    1                                                          UPPER WIDTH LIM    10                                                         UPPER WIDTH NOMNL  4                                                          UPPER WIDTH THRSH  .6                                                         ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        ACCEL/DECEL SUBROUTINE                                                                           PROB 3                                                     PARAMETERS         C14                                                        ______________________________________                                        DEGRADE MAX        10                                                         R.M.S. DVSR        .1                                                         R.M.S. EXP         1                                                          R.M.S. NOMNL       .8                                                         WIDTH DGRD         4                                                          WIDTH LO LIM       6                                                          WIDTH THRSH        .08                                                        ZERO CROS DVSR     2                                                          ZERO CROS EXP      1                                                          ZERO CROS NOMNL    10                                                         ZERO CROS THRSH    .1                                                         ______________________________________                                    

Primary Pulse Width

If the sign is correct, an affirmative result of test 2 reaches a seriesof steps 3 in which: the beginning sample is set equal to the thresholdsample; a threshold value for use in the width/peak subroutine 4 is setequal to the width threshold (which may vary as set forth in Table 2hereinafter); and the width A.G.C. command is set. Then the width/peaksubroutine 4 is called, the output of which includes the beginningsample of the primary pulse, the end sample of the primary pulse, and athreshold varied with A.G.C.. For use later in the narrow pulsesubroutine, local factors are retained in a series of steps 5: a pulsebeginning sample, an end sample, and A.G.C. threshold are set equal tothe beginning sample; end sample, and A.G.C. threshold found in thesubroutine 4. The final pair of steps 5 provide a beginning of thepost-R.M.S. interval equal to the pulse end sample, and the end of thepost-R.M.S. interval as a maximum sample, for use later on in thesubroutine, regardless of which way the subroutine advances. Then a test6 determines if a pre-R.M.S. divisor is greater than unity. Referring toTable 2, it can be seen that the parameters for probe 2, category 5include a pre-R.M.S. divisor of 1.04. Having a value greater than oneidentifies the fractional portion of the pre-R.M.S. divisor as an A.G.C.multiplicand. Thus, if test 6 is affirmative (which it would be in thecase of probe 2, category 5), a step 8 will provide, for internal use, apre-R.M.S. divisor equal to the product of the fractional portionprovided to the subroutine times the absolute value of the magnitude ofthe peak of the primary pulse found by the width/peak subroutine 4. Thesame applies with respect to the post-R.M.S. divisor which is greaterthan one for category 5 of probe 2 as well as for category 3 of probe 3.In such case an affirmative result of test 9 causes the post-R.M.S.divisor to be reconstituted in step 10 to be equal to the product of thefractional portion of the divisor times the absolute value of themagnitude of the peak of the primary pulse as determined by the widthpeak routine of FIG. 2. For other categories against which a samplerecord is being compared by the narrow pulse routine, the steps 8 and 10are bypassed.

In FIG. 25a, a test 12 compares the width of the pulse determined by thewidth/peak subroutine 4 with a primary pulse width limit. If the pulseis too wide, an affirmative result of test 12 will cause the callingprogram to be reverted to through a return point 13. Otherwise, thecategory is degraded on width by a plurality of steps 14 setting: themeasured parameter equal to the width of the pulse found by thewidth/peak subroutine 4; the nominal factor equal to the primary pulsenominal width of Table 2; the degradation equal to the width exponent ofTable 2; and the sensitivity equal to the primary pulse divisor of Table2. Then the degrade subroutine 15 is called and the degrade factor isupdated for this sample record as a consequence.

Following Peak

In the next part of the narrow pulse subroutine in FIG. 25a, a search ismade for a following peak. A series of steps 16 establish the criteriafor the search: setting the local pulse end sample value equal to theend sample plus one (one sample higher in number than the sampleidentifying the end of the primary pulse as defined by the width/peaksubroutine 4); setting the beginning sample for the search equal to thepulse end; setting the end sample for the search equal to the maximumsample (sample number 104 in the present example); resetting the reversecommand (so that a forward search will be made at sucessively highersample numbers); setting the sense command equal to zero, meaning thateither positive or negative following pulses should be recognized; andsetting the threshold equal to the following peak threshold of Table 2.Then the following peak subroutine 18 is called.

The program continues in FIG. 25b by a test 19 which determines if afollowing peak has been found. If S peak is equal to zero, this means nofollowing peak has been found, so an affirmative result of test 19 willreach a step 20 in which the degradation value is updated by adding toit some penalty factor for the opposite pulse being absent, as in Table2. In Table 2, only three categories show a desire for a following pulseof opposite polarity, the other four categories are indifferent to thatfact. If there is a following peak, a negative result of test 19 willreach a series of steps 21 which set up the characteristics forperforming the width/peak subroutine 22 with respect to the followingpulse: the beginning sample is set to the sample of the peak of thefollowing pulse; the threshold is set equal to the A.G.C. thresholddetermined in performance of the width/peak subroutine 4 (FIG. 25a); andthe width A.G.C. command is reset (so that the next performance of thewidth/peak subroutine 22 will not perform A.G.C. on the threshold andwill only pass through one time). Following performance of thewidth/peak subroutine 22 in FIG. 25b, a step 23 defines the separation(as shown in FIG. 27) between the primary pulse and the following pulseas the difference between the beginning sample of the following pulseand the pulse end (one sample higher than the end of the primary pulseas set in step 5 of FIG. 25a). Then a step 24 determines if thefollowing pulse is of the same polarity as the primary pulse (FIG. 28),or if it is of the opposite polarity thereto (FIG. 26). This is achievedby multiplying the sign of the primary pulse for the category beingexamined times the value of the peak of the following pulse. If they areof opposite polarity, the product will be negative and an affirmativeresult of test 24 will reach a test 25 to determine if the separationbetween the pulses is greater than an opposite pulse separation lowlimit (FIG. 27). This is because a following pulse of an oppositepolarity in a recognized category (such as those illustrated, forexample, in FIGS. 57 and 58) will typically be overshoots of the primarypulse. If they are overshoots, they should be very close together.Reference to Table 2 shows that a three sample limit has been foundreasonable to test for overshoots. On the other hand, if the separationis greater than the opposite pulse separation low limit, this means thatthe following pulse is not related to the primary pulse, and that theprimary pulse is therefore isolated.

In FIG. 25b, if the result of test 24 is negative, a step 26 willdegrade the pulse by the opposite pulse absent degradation factor, whichis seen to be significant in three of seven categories in Table 2. Theseare categories which require overshoot in all cases. And then a test 27determines if separation is less than a same polarity separation lowlimit, as seen in FIG. 28. Reference to Table 2 shows that this is asomewhat higher limit ranging from seven to thirteen samples in width.If pulses of the same polarity are too close together, this belies theisolated syntactic narrow pulse which relates to the categories whichcan satisfy the narrow pulse subroutine of FIG. 25. Therefore, anaffirmative result of test 27 will cause the calling subroutine to bereverted to through a return point 28, rejecting the present category asa contender. But if the pulses are either of the same polarity andsuitably separated, or if opposite polarity and suitably separated, theneither a negative result of test 27 or an affirmative result of test 25will reach a test 29 to see if the pulses are so sufficiently separatedthat no degradation results from having two isolated pulses in the samesample record, as shown for two positive pulses in FIG. 29. In test 29,the separation of the pulses is compared against a separation highlimit, which is twenty six samples in all of the examples of Table 2.This is because any additional pulses which are truly separated from theprimary pulse are of no interest in classifying the pulse one way or theother, they are simply additional events which have been sensed or theyare rapid repeats of the same event. On the other hand, if the pulsesare less than 26 samples apart as seen in FIG. 30, then degradation iseffected, depending on how much closer than 26 samples apart they are,by a negative result of test 29 reaching a series of steps 30 which setup the characteristics for running the degrade subroutine 31.Specifically: the measured value is set equal to separation; the nominalvalue is set equal to the separation high limit (the same value used intest 29); the degradation is set equal to the separation exponent andthe sensitivity is set equal to the separation divisor, all as set forthin Table 2 for the various categories. Then the sample record isdegraded by the degrade subroutine 31.

In FIG. 25b, if the pulses are of opposite polarity and sufficientlyclose together so as to be considered to be a primary pulse with anovershoot, a negative result of test 25 will reach a step 32 whichupdates the end of the pulse to be the end of the opposite polaritypulse by causing the pulse end to be set equal to one greater than theend sample determined for the following pulse in the width/peaksubroutine 22. Since the primary pulse and the opposite polarityfollowing pulse have been determined to be a single pulse, separation isnot a degradation factor, but rather the width of the following pulseis. And then the width is compared in a test 33 against a followingpulse width limit to be sure it is no wider than the permitted overshootfor the particular category under consideration. If the overshoot is toowide as shown in FIG. 31, then the calling program is reverted tothrough a return point 33a. But if the overshoot is within limits, anegative result of test 33 reaches a plurality of steps 34 to establishthe characteristics for degrading the sample record onfollowing-pulse-width by calling the degrade subroutine 35. In steps 34,the measured value is set equal to the width of the following pulse asfound in the width/peak subroutine 22: the nominal value is set equal tothe following pulse nominal width; the degradation is set equal to thewidth exponent; and the sensitivity is set equal to the following pulsedivisor, all as set forth in Table 2 for the various categories. Then,the degrade subroutine 35 is called to degrade the pulse based upon thewidth of the overshoot.

Post Pulse R.M.S. Noise

In FIG. 25b, following either of the appropriate degrade subroutines 31,35, the end of the post-pulse R.M.S. interval is redefined, in the casewhere there is a following pulse. If the following pulse is a separatepulse, the post-pulse R.M.S. interval is the separation between the twopulses. Therefore, in a step 36, the end of the post-R.M.S. interval isset equal to the minimum of either the maximum sample or one less thanthe beginning sample of the following pulse, as in FIG. 29. On the otherhand, if the following pulse is simply an overshoot of the primarypulse, then the post-pulse R.M.S. interval extends beyond the overshoot.However, to guard against the case where the wave shape may have aslowly increasing D.C. component near the end of the sample record, amaximum post-R.M.S. interval (seen in Table 2 to be 26 samples for theexemplary categories herein) is examined. This begins at the end of thecomposite pulse (including the primary pulse and the following pulseovershoot) and can extend no farther than the post-R.M.S. maximuminterval, as seen in FIG. 26. Thus, the minimum is taken in a step 37because the post-R.M.S. interval added to the pulse end could possiblyextend beyond the end of the entire record (particularly in the case ofdownstream probes whose records have been captured at a time framedependent upon the exceedance of a threshold by an upstream probe). Onthe other hand, in FIG. 25b, if there were no following pulse, theaffirmative result of test 19 passing through step 20 leaves the end ofthe post-pulse R.M.S. interval equal to the maximum sample as set instep 5 of FIG. 25a.

The narrow pulse subroutine continues in FIG. 25c by presetting thepre-pulse R.M.S. value and post-pulse R.M.S. value to zero, in steps 38.Then a test 39 determines if the pulse beginning is greater than 1. Ifit is not, there is no pre-pulse R.M.S. interval and so no R.M.S. valuecan be obtained therefor. But if it is greater than 1, steps 40 set thebeginning sample equal to 1 and the end sample equal to the pulsebeginning of the primary pulse, which was saved in the first of thesteps 5 in FIG. 25a, following the first utilization of the width/peaksubroutine 4. In FIG. 25c, following the steps 40, the R.M.S. program 41is called to provide an indication of the magnitude of R.M.S. noisebefore the primary pulse. This is saved as the pre-pulse R.M.S. value ina step 42. Then a test 43 determines if the end of the post-R.M.S.interval is greater than either the end of the primary pulse which isestablished a pulse end in the second of the steps 5 in FIG. 25a, or theend of a composite pulse with overshoot, which is saved in a step 32 inFIG. 25b. If it is not, there is no post-R.M.S. interval so no R.M.S.value can be obtained. But if the end of the post-R.M.S. interval is ata higher sample number than the end of the primary or composite pulse,the beginning sample is set equal to the end of the pulse and the endsample is set equal to the end of the post-R.M.S. interval, in a pair ofsteps 44. Then the R.M.S. subroutine 45 is called and the R.M.S. noisevalue is saved in a step 46 as the post-pulse R.M.S. value.

In FIG. 25c, a series of steps 47 set up the criteria for degrading thepulse on the basis of pre-pulse R.M.S.. The measured value is taken asthe pre-pulse R.M.S. value: the nominal value is set equal to zero; thedegradation is set equal to the R.M.S. exponent of Table 2; and thesensitivity is set equal to the pre-pulse R.M.S. divisor of Table 2.Then the degrade subroutine 48 is called. Degrading of the pulse on itspost-pulse R.M.S. noise is achieved by steps 49 setting the measuredquantity equal to the post-R.M.S. noise and the sensitivity equal to thepost R.M.S. divisor, followed by calling the degrade subroutine 50 onceagain. The pre- and post-pulse R.M.S. noise provides a discriminantagainst gross signals with a sufficient, narrow pulse in them, such asshown in FIG. 32 and FIG. 33; these may be examples of abnormalafterburner chop (FIG. 78) and rub strip peel-off (FIG. 62),respectively.

In the narrow pulse subroutine of FIG. 25, degradation occurs, for anygiven record sample to which the subroutine is applied on four or fivedifferent parameters: first, the primary pulse width (14, 15); oppositepulse absent (20); or following pulse width (34, 35), or separation (30,31); third, if there is a following pulse of the same polarity, it mayadditionally be degraded for opposite pulse absent (26); fourth, it isdegraded for pre-and post-R.M.S. (47-50). Thus there may be asignificant degradation number following the R.M.S. degradation in FIG.25c.

In order to determine the relative degree to which any particular recordsample fits a category for which the narrow pulse subroutine has beencalled, the quality factor, Q, is calculated in a step 51 in FIG. 25c.This is determined by subtracting from unity the ratio of thedegradation which has occurred to the maximum degradation which canoccur. The maximum degradation which can occur for the variouscategories is set forth at the top of Table 2. Then, in case thedegradation has exceeded maximum degradation, a test 52 determines if Qis less than zero. If it is, a step 53 sets Q for the given categoryequal to zero; if not, a step 54 sets Q for the particular categoryequal to the value of Q calculated in step 51. And then the callingsubroutine (one of FIG. 10-FIG. 12) is reverted to, through a returnpoint 55.

Wide Pulse Subroutine--FIG. 34

Pulse Width

The wide pulse subroutine of FIG. 34 is similar to the narrow pulsesubroutine of FIG. 25, in many respects. The wide pulse subroutine isreached in FIG. 25a through an entry point 1 and a plurality of steps 2:reset an opposite following pulse flag; set the width A.G.C. command;set the beginning sample equal to the sample of record thresholdcrossing; and set the threshold equal to the width threshold of Table 3,for the particular parameter being examined. Then a test 3 determineswhether or not the present sample set is of the correct polarity for thecategory being tested for, as is set in steps 8 or 11 of FIG. 11 orsteps 21 or 22 of FIG. 12, as the case may be. If the value at thethreshold sample is of the wrong polarity, a negative result of test 3will cause the program to revert to the calling routine through a returnpoint 4, thus rejecting the particular category as a candidate for thisrecord sample. But if the polarity is correct, an affirmative result oftest 3 will reach the width/peak subroutine 5. The parameters determinedin the width/peak subroutine 5 are saved for later use in the wide pulsesubroutine, in a series of steps 6: the pulse beginning sample is setequal to the beginning sample determined in the subroutine 5; the pulseend sample is set equal to the end sample determined in the subroutine4; the primary pulse width is set equal to the width determined in thesubroutine 5; the primary pulse width is set equal to the widthdetermined in the subroutine 5; the total pulse width is set equal tothe width determined in the subroutine 5; an R.M.S. divisor is givenA.G.C.-type treatment by multiplying it by the value of the peak foundin the subroutine 5; the value of the peak of the primary pulse is setequal to the value of the peak sample found in the subroutine 5; and theA.G.C. width threshold is memorized as the threshold determined (withthe width A.G.C. command set) in the subroutine 5. Then a test 7determines if the primary pulse upper width limit is zero or not.Reference to Table 3 shows that only category 4 of probe 3 requires aminimum width at the upper extremity of the pulse since it is the onlycategory of the present example which has a non-zero primary pulse upperwidth limit. An example of category 4 for probe 3 is illustrated in FIG.72. If the primary pulse upper width limit is non-zero, a negativeresult of test 7 reaches a series of steps 8 wherein the beginningsample is set equal to the sample number of the peak found in thesubroutine 5; the threshold is set equal to the upper width thresholdtimes the absolute value of the magnitude of the peak found in thesubroutine 5; and the width A.G.C. is reset. Then the width/peaksubroutine 10 is called to determine the width of the upper part of thepulse. The width determined in the subroutine 10 is compared in a test11 with the primary pulse upper width limit (see FIG. 35) as set forthin Table 3, which is a low limit on what should be a rather square pulse(e.g., the uncorrelated-2 category of FIG. 71), and if the width is notadequate, an affirmative result of test 11 will cause the callingroutine to be reverted to through a return point 12. If desired forfurther discrimination between categories (e.g., to reject normalafterburner chop, FIG. 79), upper width limits may be added to more ofthe categories in Table 3. In the event that there is no constraint onthe upper width, an affirmative result of test 7 will bypass the portionof the program 8-12 relating to the upper width.

Following Pulse

The wide pulse subroutine continues in FIG. 34b with a series of steps14 that: set a beginning sample equal to one sample higher than thenormal end of the primary pulse, as found in subroutine 5 and memorizedin the second of the steps 6; the reverse flag is reset, so that thenext peak to the right (or higher sample number) will be searched for; athreshold is set equal to the peak threshold of Table 3; and the sensecommand is set to zero, meaning that either a positive-going or anegative-going following pulse should be recognized; then the followingpeak subroutine 15 is called, after which separation is preset in a step16 to be equal to the maximum sample (104 in this example).

In FIG. 34b, a test 17 determines if a following peak has been found ornot. If the sample number of the peak is equal to zero, this means thatno following peak has been found. Otherwise, a negative result of test17 will reach a series of steps 18 in which: the beginning sample is setequal to the sample of the peak found for the following peak in thesubroutine 15; the threshold is set equal to the A.G.C. width thresholdprovided by running the width/peak subroutine 5 in FIG. 34a; and thewidth A.G.C. is reset. Then the width/peak subroutine 19 is called andthe separation is updated to be equal to the beginning sample of thefollowing pulse (determined by the width/peak subroutine 19) minus thepulse end of the primary pulse (determined by the width/peak subroutine5, FIG. 34a, and memorized in the second of the steps 6 in FIG. 34a in astep 20), as shown in FIG. 36.

The next portion of the wide pulse subroutine in FIG. 34b concernsitself with three aspects of pulse shapes in the sample record. First,the primary pulse may be wider than the width determined by thewidth/peak subroutine (5, FIG. 34a). This can occur if there is a falsedip in the pulse as a consequence of noise. This phenomenon may bevisualized by considering the wave shape of high turbine first stageblade erosion shown in FIG. 63. Therein, if the positive going spike inthe middle of the negative pulse were a little more positive as in FIG.82, it could fall within the pulse width threshold and the width wouldhave been determined to be about half of the true width. Thus, thesubroutine of FIG. 34b senses closely adjacent following pulses of thesame polarity as being part of the primary pulses; it then concatenatesthe two pulses and recomputes the overall pulse width. A second featurewhich the subroutine of FIG. 34b is concerned with is that somecategories (such as those shown in FIG. 63-FIG. 65) do not normally havefollowing pulses, so the presence of a following pulse is utilized as adegradation factor for the given category, unless the following pulse iswidely separated from the preceding pulse, in which case it can beignored as a separate, unrelated event as in FIG. 38. And finally, ifthere is a following pulse of an opposite polarity, and then a thirdpulse of the original polarity, the third pulse is treated as anindependent pulse, as in FIG. 39. Whenever two, closely adjacent pulsesof the same polarity are concatenated (whether primary or opposite,following pulses), the search for further pulses must continue (as inFIG. 38).

In FIG. 34b, a test 22 determines if the separation between the primarypulse and the following pulse is less than a separation low limitprovided from Table 3 by the calling routine. Generally, the wider thepulse of any category can be, the larger the separation can be and stillconsider the pulses to be adjacent. If the pulses are adjacent, anaffirmative result of test 22 will reach a test 23 to see if the sign ofthe peak value of the following pulse is the same as the sign for thecategory being tested (remembering that the program exits at the top ofFIG. 25a if the primary pulse is not of the correct category sign).Assuming that the pulses are of the same polarity, an affirmative resultof test 23 reaches a test 24 which determines if this is a third pulsefollowing a second pulse of opposite polarity to the primary pulse, asin FIG. 39. Initially, the opposite following pulse flag is always reset(steps 2, FIG. 34a) so that a negative result of test 24 will reach aseries of steps 25 in FIG. 34b, to concatenate the pulses, as in FIG.37. First, the pulse end (initially set at the end of the primary pulse)is now updated to be equal to the end sample of the following pulse, asdetermined by the width/peak subroutine 19 (FIG. 34b). The primary pulsewidth (previously retained in steps 6 as the width of the primary pulsefound in the width/peak subroutine 5, FIG. 34a) is recomputed as beingthe interval from the end sample of the following pulse to the beginningsample of the primary pulse; the total pulse width is similarlyrecomputed. Then the peak magnitude of the following pulse (from thesubroutine 19, FIG. 34b) is compared in a test 26 with the pulse peakretained as the peak value of the primary pulse (5, 6, FIG. 34a). If thesecond part of the pulse has a higher peak as in FIG. 38, the pulse peakis updated in a step 27; otherwise, step 27 is bypassed.

At this point of the subroutine of FIG. 34b, the description has assumedthat there has been a pair of closely adjacent pulses of the same sign.Therefore, the primary pulse has been updated to include both of them.Now it is still necessary to determine if there are any true followingpulses of either the same or opposite sign. In the case of second probecategories 1, 2 and 3 (shown in FIGS. 62-64) following pulses are notdesirable; in the case of third probe categories 5, 6 and 7 (illustratedin FIGS. 73-75) following pulses of an opposite sign are mandatory.Since the wide pulse subroutine is used for all of these catagories, ithas the capability of going forward and looking for additional pulses.

The subroutine of FIG. 34b thus reverts to the steps 14 where thebeginning sample for searching for a following peak is set one samplehigher than the pulse end of the concatenated composite pulse. The stepsand tests 14-20 are repeated to find a following pulse, and to determineits width and its peak value. Assume again that a closely adjacentfollowing pulse is found, so that test 22 is again affirmative. Assumefurther that this pulse is opposite to the polarity of the primary pulseas in FIG. 40, so that test 23 is negative. In those cases (e.g., FIG.72-FIG. 74) which require contiguous pulses of opposite polarity, theend of the overall pulse will be the end of the following, oppositepulse. Thus, a step 30 updates the pulse end to equal the end sample ofthe following pulse found in the most recent pass through the width/peaksubroutine 19. Then a test 31 determines if the opposite following pulseflag has been set or not. Initially, it has not, so a negative result oftest 31 reaches a pair of steps 32 where the opposite pulse beginningsample is set equal to the beginning sample found for the followingpulse in the most recent pass through the width/peak subroutine 19; and,the opposite following pulse flag is set. Then, in steps 33, thefollowing pulse width is calculated (see FIG. 40) as equal to the endsample of the most recently found following pulse minus the oppositepulse beginning: and, the total pulse width is updated as being equal tothe end sample of the most recently found following pulse minus thepulse beginning which was established for the primary pulse (5, 6, FIG.34a).

In the example being considered, it is assumed that there were twoclosely adjacent positive pulses (which were concatenated into a single,wider positive pulse) followed by an adjacent negative pulse (or viceversa). It is still possible that there is another closely adjacentnegative pulse (FIG. 41) which may be concatenated with the one whichwas just found, or there may be an additional positive pulse (FIG. 39)or an independent negative pulse (FIG. 42). Therefore, the programreverts again to the steps 14, now setting the beginning sample equal tothe pulse end of the third pulse which has been found. Then the stepsand tests 14-20 are again repeated looking for a fourth pulse. Assumingthat a fourth pulse is found and it is closely adjacent to the thirdone, test 22 will be affirmative reaching test 23. If this pulse is alsoopposite to the primary pulse, it can be concatenated with the thirdpulse simply by updating pulse end, following pulse width and totalpulse width, in the steps 30 and 33. But the original opposite pulsebeginning will be retained (FIG. 41) since the opposite following pulseflag 31 will be set and bypass the steps 32. On the other hand, if afourth pulse is found which is of the same polarity as the primarypulse, after a following pulse of an opposite polarity (FIG. 39), anaffirmative result of test 23 will reach test 24 which is affirmative,thereby treating the additional pulse as being independent (just thesame as if it were not adjacent to the opposite pulse). Whenever eithertest 22 (FIG. 42) or test 24 (FIG. 39) identifies an independent pulse(regardless of polarity), the subroutine of FIG. 34b reaches a test 35which determines if the independent pulse is sufficiently separated fromthe pulses of interest to be irrelevant in the classifying process, asin FIG. 38. If so, the separation is greater than the separation highlimit (Table 3), and an affirmative result of test 35 will bypassdegradation as a function of an independent pulse. If the pulse is tooclose (less than the separation high limit) as in FIG. 42, then anegative result of test 35 causes a series of steps 37 to establish thecharacteristics for degrading this category inversely with the extent towhich the separation between the pulses of interest and the independentpulse is less than the separation high limit. And the degrade subroutine38 is called.

In FIG. 34b, any time the subroutine returns to the steps 14 and callsthe following peak subroutine 15, if no peak is found, test 17 will beaffirmative thus bypassing test 35 and the degradation 37, 38.

The wide pulse subroutine continues in FIG. 34c with a test 40 whichdetermines if the opposite following pulse flag was set, or not. Thethird probe categories 5-7 (illustrated in FIGS. 73-75) are heavilydependent upon there being an opposite following pulse. Reference toTable 3 shows that the opposite pulse absent degradation factor is setequal to 15 for these categories, which is significant compared to thedegrade maximum of 20 for these categories. A negative result of test 40will reach a step 41 which will heavily degrade these three categoriesif there is no opposite following pulse. The other categories whichutilize the wide pulse subroutine do not require opposite followingpulses. In FIG. 34c, if test 40 is affirmative, this reaches a series ofsteps which will degrade the category for those parameters for which anopposite pulse is not normally present. Reference to Table 3 shows thatthe opposite pulse present degradation factor is significantly smallerthan the opposite pulse absent degradation factor; this means simplythat although these categories do not require an opposite followingpulse, the presence of one is only moderately indicative of categoryexclusion, so only a minor degradation is performed.

Multiple Peak Check

In FIG. 34c, the remaining steps 42 establish the conditions forsearching for multiple peaks, as is required for third probe category 7,impact induced turbine rub (FIG. 74). This acts as a discriminantagainst the third probe categories 5 and 6 (FIG. 72 and FIG. 73) whichare normal turbine rubs, in contrast with turbine rub induced by impact,of an engine fragment or ingested object, on the turbine. In the steps42: the beginning sample is set equal to the pulse beginning (thebeginning of the primary pulse set in steps 6 of FIG. 34a); the endsample is set equal to the pulse beginning summed with primary pulsewidth, thereby defining that the multiple peaks subroutine 43 will beperformed across the samples of the primary pulse, whether concatenatedfrom two adjacent pulses of the same polarity as in FIG. 42, or not;then a high threshold and a low threshold are calculated as the productof the pulse peak (established in step 6, 23a for a unitary pulse, andpossibly updated in step 27 of FIG. 34b for a concatenated primarypulse) multiplied by a multiple peak high threshold and a multiple peaklow threshold set as in Table 3. Notice that thresholds are provided forall of the categories that use the wide pulse subroutine: this is anexample of the discrimination process which requires looking formultiple peaks regardless of which category is under consideration sincethe presence of multiple peaks will absolutely rule out all of thecategories except third probe category 7: the only category in whichextra peaks are desired (bottom of Table 3). In FIG. 34c, the multiplepeaks subroutine 43 is called and a test 44 determines if extra peakshave been found or not. If extra peaks have been found, then a test 45examines the extra peaks desired parameter (bottom of Table 3) to see ifthe category being examined requires extra peaks or not. If not, thisrejects the category under consideration and the calling subroutine isreverted to through a return point 46. On the other hand, if test 44 isnegative, then a test 47 determines if extra peaks are desired. If nopeaks have been found but third probe category 7 is being considered,this rejects this category so the calling subroutine is reverted tothrough the return point 46.

Width Degradation

The portion of the wide pulse subroutine shown in the remainder of FIG.34c provides width degradation. Program flexibility is achieved bydefining any nominal width of Table 3 which is negative as a flagindicative of the fact that width degradation is not to be performed.Thus a test 50 determines if the primary pulse nominal width (Table 3)is greater than zero. If it is, steps 51 establish the conditions fordegrading the primary pulse width by calling the degrade subroutine 52.But if the primary pulse nominal width is negative, the steps 51 anddegradation routine 52 are bypassed. Then a test 53 determines if theopposite following pulse flag has been set or not. If it has, a test 54determines if the following pulse nominal width is positive. If it is,then a series of steps 55 set up the conditions for degrading thecategory as a function of the width of the following pulse, by callingthe subroutine 56. If either test 53 or test 54 is negative, thedegradation on following pulse width (55, 56) is bypassed. Then a test57 determines if a total pulse nominal width is positive. If it is, aseries of steps 58 set up the conditions for degrading on total pulsewidth by calling the degrade subroutine 59. But if test 57 is negative,degrading on total pulse width (58, 59) is bypassed. Notice in Table 3that the total pulse nominal width is indicated as being ×1 for all ofthe categories which are examined by the wide pulse subroutine. This isindicative of the flexibility of the present embodiment: total pulsewidth may in some cases be a useful, discriminating degradation factor,although in the present examples it is not.

R.M.S. Noise

The remainder of the wide pulse subroutine illustrated in FIG. 34d isconcerned with measuring the pre-pulse interval R.M.S. noise and thepost-pulse interval R.M.S. noise. In the present example, pre andpost-pulse R.M.S. noise is measured for all of the categories thatutilize the wide pulse subroutine. However, such is not necessarilyrequired; if R.M.S. noise is not of interest in some category other thanthe examples herein, measuring the R.M.S. noise and degrading thecategory accordingly can be sidestepped by setting the post-R.M.S.maximum interval (Table 3) to zero. Then a test 60 would be affirmativecausing the subroutine of FIG. 34d to bypass the R.M.S. noise portions.In the examples herein, test 60 is negative and steps 61 set thebeginning sample equal to 1 and the end sample equal the pulse beginning(of the primary pulse). This causes R.M.S. noise to be calculated by thesubroutine 62 from the start of the record sample to the beginning ofthe primary pulse. In steps 63, the pre-R.M.S. interval is recorded asthe R.M.S. value determined by the subroutine 62, and the beginningsample is updated to equal one sample greater than the pulse end. Thepulse end is the end of the total pulse, and may be the end of asingular primary pulse as established in step 6 of FIG. 34a, or the endof a concatenated primary pulse as set in step 25 of FIG. 34b, or theend of a pair of opposite polarity, adjacent pulses as set in step 30 ofFIG. 23b. The R.M.S. noise is polluted by the presence of an additionalpulse following the pulse of interest. Therefore, the separation betweenpulses (if there is more than one pulse in a record) is compared withthe post-R.M.S. maximum interval. The separation value used at thispoint in the subroutine may be 104 (the maximum sample) as set in step16 of FIG. 34b, in the case where there are no independent pulsesfollowing a simple or concatenated primary pulse. When there is noindependent following pulse, step 17 bypasses the remainder of FIG. 34bso the separation is set at the maximum sample (104 samples). On theother hand, when independent pulses are found by a negative result oftest 22 or an affirmative result of test 24, the iterative process ofFIG. 34b ends. Thus, any separation found in step 20 for concatenated oropposite pulses eventually is overwritten by the maximum sample of step16, which is retained in the case that test 17 indicates no followingpeaks, or is further overwritten by step 20 when independent additionalpulses are found. Thus it is, that the separation utilized in test 64 ofFIG. 34d can only be the maximum sample or the separation between apulse of interest and an independent pulse. In the general case, theseparation will be that set in step 16 of FIG. 34b causing a negativeresult of test 64 to reach a step 65 in which the end sample is taken tobe that which is separated from the end of the pulse by the post-R.M.S.maximum interval. The post-R.M.S. maximum interval is utilized to avoidtaking R.M.S. noise at the highest sample numbers of a record samplehaving a relatively narrow pulse, since there is a tendency for anincrease in D.C. drift that pollutes the R.M.S. noise factor at the highend of the sample (as described with respect to FIG. 26, hereinbefore).

If there is an independent following pulse, and if it is closer to thepulse of interest than the post-R.M.S. maximum interval, an affirmativeresult of test 64 in FIG. 34d will reach a step 66 in which the endsample is defined to be that just ahead of the following pulse. Ifeither step 65 or step 66 sets the end sample too high, this will bedetected by a test 67 which compares the defined end sample with themaximum sample. If it is too high, an affirmative result of test 67 willreach a step 68 where the end sample is simply set equal to the maximumsample. Otherwise, step 68 is bypassed. Then the R.M.S. subroutine 69 iscalled and the value determined therein is set as the post-R.M.S. valuein a step 70. A plurality of steps 71 establish the conditions fordegrading on the pre-pulse R.M.S. noise by calling the degradesubroutine 72, and then a step 73 establishes the same conditions butfor degrading on post-pulse R.M.S. noise by calling the degradesubroutine 75.

In FIG. 34d, when R.M.S. noise has been considered, the sample recordhas its quality factor, Q, calculated in step 76 as unity minus theratio of the accumulated degrade factor to the maximum degradationpermitted for the category. If the degradation is more than the maximum,Q becomes negative, and a test 77 senses that and causes Q for thepresent category to be set equal to zero in a step 78. Otherwise, anegative result of test 77 reaches a step 79 where the Q for thecategory under consideration is set equal to the Q calculated in step76. And then the calling program is reverted to through a return point80.

Surge Subroutine--FIG. 43

The surge subroutine of FIG. 43 is utilized to recognize first probecategory 3, compressor surge, as illustrated in FIG. 59. The waveformresulting from electrostatic charge during surge/stall conditions ischaracterized by a succession of large-amplitude swings, from positiveto negative. Many of the swings are abrupt, occurring within one or twosamples. It is detected by simply counting the number of swings of largeamplitude (4 volts, Table 4). In FIG. 43, the surge subroutine isreached through an entry point 1 and a plurality of steps 2 set thebeginning sample equal to the first sample of the record and the endingsample equal to the maximum sample; a threshold is set equal to the zerocrossing threshold (Table 4) and the zero crossings subroutine 3 iscalled. The number of zero crossings determined by the subroutine 3 iscompared in a step 4 with a zero crossing low limit (Table 4). If thereare insufficient zero crossings, an affirmative result of test 4 causesthe calling program to be reverted to through a return point 5, thuscausing the Q for the surge category for the present record to remainzero.

In FIG. 43, if the record has an adequate number of zero crossings, anegative result of test 4 will reach a series of steps 5 to set up theconditions for degrading the category on the number of zero crossings bycalling the degrade subroutine 6. And the quality factor for the surgecategory is determined as unity minus the ratio of the zero crossingdegradation to the maximum degradation permitted for surge, in a step 7.Then a test 8 determines if the degradation has exceeded maximum,resulting in a negative value of Q. If so, an affirmative result of test8 reaches a step 9 which sets Q for this category equal to zero.Otherwise, a negative result of test 8 reaches a step 10 where the valueof Q for the surge category is set equal to the Q calculated in step 7.And then the calling program is reverted to through a return point 5.

Notice that the surge category is tested for only zero crossings.Comparison of the parameters in Table 4 for the surge subroutine withthe parameters in Table 6 for the loose probe/rub strip subroutineindicate how surge can be recognized on the single parameter.Particularly, the frequency content is relatively low, having a nominalzero crossing of 8. Furthermore, the excursions must be rather violent,having a zero crossing threshold of 4 volts. This compares with muchhigher frequency content (nominal zero crossings of 45 and 60, etc.)with very low zero crossing thresholds (0.3) for the categories setforth in Table 6. Therefore, the soft degradation of the presentinvention becomes significant in determining whether first probecategory 3 compressor surge or first probe category 5 abradable sealingestion has been sensed by the first probe.

Loose Electrode Subroutine--FIG. 44

The loose electrode subroutine of FIG. 44 is utilized in searching forfirst probe category 4, as illustrated in FIG. 60, which is indicativeof the electrode being loose within a probe (such as probes 1 and 2 inFIG. 1). The loose electrode wave shape is characterized by fairly longpositive and negative excursions, at least one of which has to be longerthan 20 milliseconds (26 samples, at a 1.3 KHz sampling rate), Table 5,WIDTH LO LIM. The excursions may be of varying magnitudes, and may haveextremely low slopes of increasing and decreasing magnitude. The widthdetection is therefore difficult; this is accommodated by utilizing awidth threshold which is a very small decimal fraction as an A.G.C.multiplicand against the value of the first peak of the pulse.Additionally, the portion of the wave shape which may have triggered therecord threshold may be a very short duration excursion, the longduration excursion may follow it, as in the example set forth in FIG.60: this is accommodated by looking for at least an additional pulsefollowing the primary pulse.

In FIG. 44, the loose electrode subroutine is reached through an entrypoint 1, and a pair of steps 2 set the beginning sample equal to 1 andthe end sample equal to maximum sample, for the purposes of performingthe zero crossings subroutine 3. Then a series of steps 4 set thebeginning sample equal to the sample number of the record thresholdcrossing, a threshold is set equal to the width threshold (of Table 5),and the width A.G.C. command is reset so that the width/peak subroutine5 will only be passed through one time, simply to determine the peakvalue of the primary pulse. This is used in steps 6 to establish thethreshold for actually determining the width of the primary pulse of therecord, in a second calling of the width/peak subroutine 7. The steps 6also reestablish the beginning sample for the width/peak subroutine 7 asthe sample of the record threshold crossing (since the previous passthrough the width/peak routine 5 established the beginning sample as thestart of the pulse). And a following pulse flag, utilized elsewhere inFIG. 44 as described hereinafter, is reset. The A.G.C. threshold isprovided externally of the width/peak subroutine to enable looking forthe width of successive pulses, iteratively, in the subroutine 7. Afterthe width/peak subroutine 7 is called, utilizing the A.G.C. widththreshold, the width determined for the primary pulse is compared in atest 8 with a width low limit (Table 5). Assume for discussion that thewidth of the primary pulse is insufficient to identify a loose electrodewave shape. A negative result of test 8 will reach a test 9 to determineif the following pulse flag has been set or not. Initially, it has notbeen, because of having been reset in the steps 6. A negative result oftest 9 reaches a series of steps 10 in which: the beginning sample (forthe following pulse) is set equal to the end sample of the primary pulsedetermined from the preceding operation of the width/peak subroutine 7;the end sample is set equal to the maximum sample; the threshold is setequal to the following peak threshold; the sense command is set equal tozero, so that either positive or negative peaks can be found; and thereverse command is reset so that the following peak subroutine 11 willproceed rightwardly. If no following pulse is found by the subroutine11, an affirmative result of a test 12 will cause the program to exit(thereby rejecting loose electrode as a possible category for the samplerecord). It does this by causing the calling program to be reverted tothrough a return point 13. On the other hand, if a following pulse isdetected by the subroutine 11, a negative result of test 12 will reachsteps 14 in which: the beginning sample is set equal to the sample ofthe peak so found; and the following pulse flag is set. Then the widthpeak subroutine 7 is called again, this time to determine the width ofthe following peak. If the width of the following peak is inadequate, anegative result of test 8 will reach test 9 which this time isaffirmative, causing the calling program to be reverted to through thereturn point 13, thus rejecting loose electrode as a possible categoryfor the present sample record. If desired, steps 14 could increment acounter and test 9 could compare the counter to reject a record aftertesting the width of 3, 4 or more narrow pulses. Such has not been foundnecessary, as yet.

If (in either the first or second pass through the subroutine 7) a widthin excess of the width low limit is indicated, an affirmative result oftest 8 reaches a test 16 in which the number of zero crossings (found bythe subroutine 3) is compared against a zero crossing high limit. Ifthere is too high a frequency content, an affirmative result of test 16causes the calling program to be reverted to through the return point13, thus rejecting loose electrode as a possible category for thecurrent sample record. The number of zero crossings is used as adiscriminant against other waveshapes which may have a wide first orsecond pulse, such as the surge waveshape of FIG. 59. If there were notfound to be an excessive number of zero crossings, a negative result oftest 16 will reach a series of steps 17 which set up the conditions fordegrading the pulse record as a function of zero crossings in thedegrade subroutine 18. Then the quality factor, Q, for the looseelectrode category is established in a step 19 as unity minus the ratioof the degradation factor to the maximum degradation permitted for thiscategory. Then a test 20 determines if the quality factor is negative;if it is, the quality factor for the current category is set equal tozero in a step 21; otherwise, the quality factor for this category isset in a step 22 to equal the value of Q established in step 19. Andthen the calling program is reverted to through the return point 13.

Loose Probe/Rub Strip Subroutine--FIG. 45

The loose probe/rub strip subroutine of FIG. 45 is utilized to sense aloose probe (such as probes 1 or 2 in FIG. 1) and to sense the ingestionof an abradable seal (rub strip) which has peeled loose from thecompressor stage of the engine. The loose probe/signature (FIG. 61) isprimarily random noise having a relatively low frequency structure. Therub strip results in a succession of very narrow pulses that merge intoa high frequency signature (FIG. 62) with an R.M.S. level of nearly onevolt. Thus, two parameters are utilized for these categories: one isR.M.S. noise and the other is the number of zero crossings (frequencycontent). In order to reduce the chance of falsely recognizing a wide ornarrow pulse with a high noise content as being one of these twocategories, the width of the primary pulse is excluded from the R.M.S.noise calculations. Referring to FIG. 46, a pulsatile signal withsignificant, high frequency noise could satisfy both the zero crossingand R.M.S. criteria of a loose probe or rub strip signature. Due to theenergy of the pulse, the R.M.S. value over the 104 samples of the recordcould be around one volt. But, by excluding the pulse area from theR.M.S. calculation, the R.M.S. value will be very low and easilydiscriminated against. On the other hand, reference to FIG. 47 showsthat exclusion of the primary pulse of either a loose probe or rub stripsignature will have little effect on R.M.S. noise taken across the restof the record.

R.M.S. Noise

The loose probe/rub strip subroutine is reached in FIG. 45a through anentry point 1, and a first series of steps 2 set the threshold for thewidth/peak subroutine 3 equal to one-tenth of a volt; the beginningsample is set equal to the sample of the probe threshold crossing; thewidth A.G.C. is reset; and the values of pre-pulse R.M.S. noise andpost-pulse R.M.S. noise are both preset to zero. After calling thewidth/peak subroutine 3, in a series of steps 4, a pre-pulse interval isidentified as being from the beginning of the record to the beginningsample of the pulse found by the width/peak subroutine 3, referred to asS1, which also identifies the end sample of the pre-pulse R.M.S.interval. The post-pulse R.M.S. interval is established in the secondone of the steps 4 as S2, which is the entire sample record followingthe end sample of the pulse found by the width/peak subroutine 3; andthe pulse end is memorized as the end sample found in the subroutine 3.Then a test 5 determines if S1 is greater than 1, meaning that there isin fact a pre-pulse R.M.S. interval. If it is, an affirmative result oftest 5 reaches steps 6 in which the beginning sample is set equal to 1,and the end sample is set equal to S1 to establish the conditions forrunning the R.M.S. subroutine 7. The R.M.S. value found by thesubroutine 7 is preserved as the pre-pulse R.M.S. in a step 8. If S1 isnot greater than 1, a negative result of test 5 bypasses the pre-R.M.S.calculations 6-8.

To find the post-pulse R.M.S. value, a series of steps 9 set thebeginning sample equal to the pulse end memorized in steps 4 and set theend sample equal to the maximum sample of the record. Then the R.M.S.routine 10 is called to provide the post-R.M.S. value, which ismemorized in the first of a pair of steps 11. In the second of the steps11, the pre-R.M.S. value and post-R.M.S. value are added, quadratically(since they cannot be added linearly). Thus the total R.M.S. value isfound as the square root of the proportionate contribution of thepre-R.M.S. and post-R.M.S. intervals as set forth in steps 11, all in awell known fashion. Then a test 12 determines if the total R.M.S. noiseis less than an R.M.S. low limit as set forth in Table 6. If it is, anaffirmative result of test 12 will cause the calling program to bereverted to through a return point 13, thus rejecting either loose probeor rub strip (as the case may be) as a potential category for the recordbeing tested. If the R.M.S. is above the low limit, a series of steps 14establish the conditions for degradation on R.M.S. noise by the degradesubroutine 15.

Zero Crossings

The loose probe/rub strip subroutine continues in FIG. 45b with a seriesof steps 17 which set up the conditions for calling the zero crossingssubroutine 18: the beginning and ending samples are set equal to thefirst and last samples of the record, and the threshold is set equal tothe zero crossing threshold of Table 6. The number of zero crossingsfound by the zero crossing subroutine 18 is compared in a test 19 to seeif it is lower than a zero crossing low limit set forth in Table 6. Ifit is, an affirmative result of test 19 will cause the calling programto be reverted to through a return point 20, thereby rejecting theappropriate category as a candidate for the record under test. But ifthere is a sufficient number of zero crossings, then a test 21determines if there are too many zero crossings (too high a frequencycontent). If the number of zero crossings exceeds the zero crossing highlimit (Table 6) an affirmative result of test 21 will cause the callingprogram to be reverted to through the return point 20. If the number ofzero crossings is suitably within the desired range, negative results ofboth tests 19 and 21 will reach a series of steps 22 in which theconditions are established for degrading the category on zero crossingsin the degrade subroutine 23. Then, the quality factor, Q, for thecategory under test is established as unity minus the ratio of the totaldegradation (effected by running the degrade subroutine 15, 23 for bothR.M.S. noise and zero crossings) to the maximum degradation permittedfor the given parameter. Then a test 25 determines if the degradationhas exceeded the maximum, and if so, a step 26 sets the quality factorfor the current category equal to zero. Otherwise, a step 27 sets thequality factor for the current parameter equal to the value of Qestablished in the step 24. And then the calling program is reverted tothrough a return point 28.

Abnormal Afterburner Chop Subroutine--FIG. 54

The abnormal afterburner chop subroutine of FIG. 54 is utilized toidentify probe 3, category 11 and category 12. Both the beginning andthe ending of an abnormal afterburner chop, believed (although not knownwith certainty) to be related to rubbing of a nozzle member duringnozzle closure, are characterized by intervals of high noise andintervals of low noise. During the start of the abnormal afterburnerchop, the low noise interval is followed by a high noise interval thatbegins abruptly with a negative excursion. At the end of the abonormalafterburner chop, a high noise interval ending abruptly in a positiveexcursion is followed by a low noise interval. The abnormal afterburnerchop subroutine of FIG. 54 utilizes the R.M.S. noise in the high noiseinterval, and the zero crossings in the high noise interval separatelyfrom the zero crossings in the low noise interval in order to identifythese categories.

Referring to FIG. 48, a normal afterburner chop (as in FIG. 79), butwith a suitably wide, high amplitude pedestal could provide a highR.M.S. noise value in the high noise interval, and could otherwise meetthe criteria of the end of abnormal chop (FIG. 78). However, byrequiring a minimum frequency content in the high noise region, thesignature of FIG. 48 can be discriminated and rejected fromconsideration as start of abnormal chop. To discriminate against rubstrip (FIG. 62) or acel/decel (FIG. 80), the absence of activity in thelow noise region is of interest. Referring to FIG. 49, D.C. drift couldprovide a high R.M.S. value in the low noise interval of a validabnormal afterburner chop signature. Therefore, low R.M.S. noise cannotbe used to discriminate against other cross signals. Instead, a low zerocrossing count (based on a suitable threshold) eliminates gross signals(FIG. 62 and FIG. 80). Referring to FIG. 50, the signature in questioncould have its final, positive pulse too close to the end of the recordto indicate whether it is a rub strip (FIG. 51) or an abnormal A/B chop(FIG. 52). Therefore, a minimum post-pulse, low noise interval isrequired, or the pulse is rejected.

The abnormal afterburner chop subroutine is reached in FIG. 54a throughan entry point 1 and in a first test 2, examines the sign set in step 23or 24 of the third probe subroutine of FIG. 12 to determine whether thebeginning of chop or end of chop is being looked for. If the sign isnegative, this means the beginning of chop is being looked for andsearching for the high noise region should begin at the lowest samplenumber and proceed to the right. Therefore, a negative result of test 2reaches a step 3 to reset the reverse flag that is utilized in thefollowing peak subroutine. If the sign is positive, an affirmativeresult of test 2 reaches a step 4 to set the reverse flag. Then a seriesof steps 5 establish the conditions for running the following peaksubroutine 7: the beginning sample is set equal to 1; the end sample isset equal to the maximum sample; and the threshold is set equal to thepeak threshold set forth in Table 7. In the case of the end of abnormalchop, because the reverse flag is set, the search for the following peakbegins at the MAX sample and ends at the first sample of the record, asdescribed with respect to FIG. 15, hereinbefore.

In FIG. 54a, after running the following peak subroutine 7, if no peakin fact has been found, an affirmative result of a test 8 will cause thecalling program to be reverted to through a return point 9, thusrejecting abnormal afterburner chop as a category for the current samplerecord. But if a peak has been found, a negative result of test 8reaches a test 9a to determine if the high noise threshold (Table 7) isgreater than unity, or not. If it is, the program definition of athreshold exceeding unity causes a step 10 to use only the decimalfraction portion thereof as a multiplicand against the magnitude of thepeak found by the subroutine 7, so as to provide an A.G.C. high noisethreshold related to the peak value of either the beginning or ending ofthe high noise region. Otherwise, step 10 could be bypassed, if desired.Similarly, steps and tests 12-17 will convert the low noise threshold,the R.M.S. low limit, and the R.M.S. nominal value to A.G.C. values ifthey are provided to the abnormal A/B chop subroutine as values greaterthan unity; otherwise, the conversion steps are bypassed. In the presentexample, the R.M.S. low limit and R.M.S. nominal values are less thanunity and therefore they are not converted to A.G.C. values as afunction of the peak value of the end excursion of the high noiseinterval.

The abnormal A/B chop subroutine continues in FIG. 54b with a test 19which determines if beginning or ending of chop is involved. If the signis negative, a negative result of test 19 reaches a series of steps 20which set: the beginning of the high noise interval equal to the sampleof the peak found by the following peak subroutine 7; the end of thehigh noise interval equal to the maximum sample; the beginning of thelow noise interval equal to the first sample; and the end of the lownoise interval equal to one sample less than the sample of the peakfound for the first excursion of the high noise interval.

On the other hand, if the sign is positive, an affirmative result oftest 19 will reach a series of steps 21 in which: the beginning of thehigh noise interval is set equal to the first sample, the end of thehigh noise interval is set equal to the sample of the peak of the finalexcursion; the beginning of the low noise interval is set equal to onesample higher than the peak of the final excursion; and the end of thelow noise interval is taken as the maximum sample. Then in a series ofsteps 22: the high noise interval is defined as the end of the highnoise interval minus the beginning of the high noise interval; the lownoise interval is set equal to the end of the low noise interval minusthe beginning of the low noise interval; the beginning sample is setequal to the beginning of the high noise interval; the ending sample isset equal to the ending of the high noise interval; and the threshold isset equal to the high noise threshold. Then the zero crossing subroutine23 is called. The number of high noise interval zero crossings is set ina step 24 to be equal to the number of zero crossings found by runningthe subroutine 23. Then, using the same beginning and ending sample, theR.M.S. subroutine 26 is called. Then, in steps 27, the beginning sampleis set to the beginning of the low noise interval and the ending sampleis set to the end of the low noise interval. The zero crossingsubroutine 28 is called with respect to the low noise interval and thenumber of zero crossings found in the low noise interval is set, in step29, to equal the number of zero crossings found in the second running ofthe zero crossing subroutine 28. Then a test 31 compares the low noiseinterval with a low noise interval limit, which is shown in Table 7 tobe 22 samples. The reason for this is if the low noise interval is tooshort, the signature could be a non-chop gross signal (as in FIG. 51);the region must be long enough to verify a low noise region. If the lownoise interval is too small, an affirmative result of test 31 will causethe calling program to be reverted to through a return point 32, thusrejecting abnormal afterburner chop as a candidate category for therecord under test. If there is a suitable low noise interval, a negativeresult of test 31 will reach a test 34 to determine if the R.M.S. noisein the high noise interval is less than an R.M.S. low limit set forth inTable 7. If it is, the calling program is reverted to through the returnpoint 32, thus rejecting abnormal afterburner chop as a candidatecategory. If there is a suitable low noise interval and suitable highnoise interval R.M.S. value, a series of steps 35 set up the conditionsfor degrading the record on R.M.S. noise by calling the degrade program36.

The abnormal afterburner chop subroutine continues in FIG. 54c with aseries of steps 37 that normalize the nominal and limit values of highnoise interval and low noise interval zero crossings counts to thelength of the interval in which they are counted. This is done byproviding values on a full-record basis (Table 7), and taking the ratiothereof for the appropriate interval. Then, a test 38 compares the zerocrossings in the high noise region against the high noise limit providedin steps 37. If there are insufficient zero crossings, an affirmativeresult of test 38 causes the calling program to be reverted to through areturn point 39, thus rejecting abnormal afterburner chop as a candidatecategory for the record under test. Otherwise, a negative result of test38 reaches a series of steps 40 which establish the conditions fordegrading the record as a function of high noise interval zero crossingsby calling the degrade subroutine 41, using the nominal value calculatedin steps 37. Then a test 42 determines if the low noise zero crossingsare greater in number than a low noise limit calculated in steps 37. Ifso, the calling routine is reverted to through the return point 39. Thepurpose of comparing on the high and low limits in an opposite fashionis because any abnormal afterburner chop must have an active high noiseregion and a fairly quiet low noise region. If the number of zerocrossings in the low noise region is not excessive, then a series ofsteps 44 establish the conditions for degrading the sample record on thenumber of zero crossings in the low noise region by calling the degradesubroutine 45, using the nominal value calculated in steps 37. And then,the quality factor, Q, for either of the abnormal afterburner chopcategories, as the case may be, is determined in step 46, as unity minusthe ratio of total degradation to maximum degradation permitted. Then atest 47 determines if excessive degradation has resulted in a negativeQ; if it has, a step 48 sets Q for the category equal to zero;otherwise, a step 49 sets Q for the category equal to the value of Qfound in step 46. Then the calling program is reverted to through areturn point 50.

Normal Afterburner Chop Subroutine--FIG. 55

The normal afterburner chop subroutine of FIG. 55 looks for a peculiarspike that occurs contemporaneously with minimum nozzle area as thenozzle is closed in shutting down the afterburner. As illustrated inFIG. 79, this pulse has a rather narrow peak sitting atop a rather widepedestal. And the pulse is also characterized by a low R.M.S. noiselevel following the pedestal. The normal afterburner chop subroutine isreached in FIG. 55a through an entry point 1 and a first test 2determines if the record under test has a positive record thresholdcrossing. If not, an affirmative result of test 2 will cause the callingprogram to be reverted to through a return point 3, thus eliminatingnormal afterburner chop as a candidate category for the record undertest. Then a series of steps 4 set up the conditions for testing thewidth of the pedestal in the width/peak subroutine 5: the beginningsample is set to the sample of the probe threshold crossing; the widththreshold is set equal to the low width threshold (of Table 8); and thewidth A.G.C. is reset, so that the width/peak subroutine 5 is passedthrough only one time with a fixed width threshold. After the width/peaksubroutine 5 concludes, in a series of steps 6: the pulse end sample isidentified as one sample greater than the end of the primary pulse foundby the subroutine 5; the low width of the pulse (the width of thepedestal) is set equal to the width of the primary pulse found by thesubroutine 5; the width threshold is calculated as the upper widththreshold times the absolute value of the magnitude of the peak found inthe subroutine 5; the R.M.S. divisor (for degrading the record on noiselevel) is calculated as the R.M.S. divisor times the absolute value ofthe magnitude of the peak found in the subroutine 5; and the beginningsample for running the width/peak subroutine 7 is set equal to thesample of the peak found in the subroutine 5. The width/peak subroutine7 is thus run to determine the width of the narrow, upper portion of thepulse. The narrow upper width constraint discriminates against singlepositive pulses followed by low noise, such as that shown in FIG. 71. Insteps 8: the upper width is set equal to the width found in thesubroutine 7; the beginning sample is set equal to the pulse end of thepedestal, as found in running the subroutine 5; the end sample is setequal to the maximum sample; the threshold is set equal to the peakthreshold; the reverse command is reset; and the sense command is setequal to zero. Then the following peak subroutine 9 is called, lookingfor any positive or negative peak beginning at the end of the pedestaland searching to the right to the end of the sample. If any peak isfound, the record is probably a strange example of acel/decel (FIG. 80),so an affirmative result of a test 10 will cause the calling program tobe reverted to through a return point 11, thus eliminating normalafterburner chop as a candidate category for the record under test.

In FIG. 55a, a test 13 determines if the number of samples between theright-hand end of the pedestal and the end of the sample record issufficient to confirm low R.M.S. noise, as described with respect toFIG. 50-FIG. 52, hereinbefore, by comparing it with a post-pulse R.M.S.interval low limit (Table 8). If there is an insufficient R.M.S.interval, an affirmative result of test 13 will bypass the measuring ofR.M.S. noise and degradation thereon. But if there is a sufficientinterval, a negative result of test 13 reaches the R.M.S. subroutine 14,utilizing the beginning and ending samples established in the steps 8. Ahigh post-pulse R.M.S. noise could be indicative of an abnormal chop, asin FIG. 53, because abnormal chops frequently have high post-pulse D.C.drift, whereas normal chops do not. If the value of R.M.S. noisedetermined by the subroutine 14 exceeds an R.M.S. high limit, anaffirmative result of a test 15 will cause the calling program to bereverted to through a return point 16, thus eliminating normalafterburner chop as a potential category for the record under test. Butif the R.M.S. noise is within limit, a negative result of test 15reaches a series of steps 17 which set up the conditions for degradingthe pulse record on R.M.S. noise by calling the degrade subroutine 18.

The normal afterburner chop subroutine continues in FIG. 55b with a test20 which determines if the necessarily narrow pulse atop the pedestal iswider than an upper width limit. And a test 21 determines if thenecessarily wide pedestal is narrower than a low width limit. If eitherof these conditions exist, the record cannot result from a normalafterburner chop. Therefore, an affirmative result of either test 20 ortest 21 will cause the calling program to be reverted to through areturn point 22, eliminating normal afterburner chop as a categorycandidate for the record under test. Then, a series of steps 24 set upthe conditions for degrading the sample record on the width of thepedestal by calling the degrade subroutine 25. And a series of steps 26set up the conditions for degrading the record on the width of the pulseatop the pedestal by calling the degrade subroutine 27. In step 28, thequality factor, Q, is calculated as unity minus the ratio of the sum ofthe three degradations to the maximum degradation permitted for thiscategory. A test 29 determines if the degradation has exceeded maximum.If it has, an affirmative result of test 29 reaches a step 30 where theQ for the category is set equal to zero. Otherwise, a negative result oftest 29 reaches a step 31 where Q for the category is set equal to thevalue of Q determined in step 28. And then the calling program isreverted to through a return point 32.

Acel/Decel Subroutine--FIG. 56

The acel/decel subroutine of FIG. 56 is utilized to recognize generallynormal acceleration/deceleration noise, as illustrated in FIG. 80.Depending upon the voltage threshold utilized for the third probe, theacel/decel subroutine can be used to recognize only excessiveacceleration/deceleration noise. This may be achieved by utilizing avoltage threshold on the third probe which is based at least in partupon the noise charactertistics of the engine, as described hereinbeforewith respect to FIG. 7. If the threshold varies with engine noise,acceleration or deceleration noise should not trip the threshold; if itdoes trip the threshold, and acceleration/deceleration noise is theindicated category, this provides an indication of some abnormality inthe engine, such as may occur if there is a cracked engine case or thelike. On the other hand, if a fixed threshold is utilized for the thirdprobe, and under rapid acceleration or deceleration the noise can exceedthe threshold, then categorizing the result as normalacceleration/deceleration is an indication of the lack of enginedistress (rather than a category identifying distress). Theelectrostatic signature of normal acceleration or deceleration iscorrelated noise on the order of 1 volt R.M.S. level, and on the orderof 100 Hz. It has no narrow spikes, but it may contain several positiveor negative excursions of 10 ms-20 ms duration. To decrease thepossibility of falsely categorizing some other, large narrow spike witha high noise content (such as a rub strip, FIG. 62, or abnormal chop,FIG. 77 or FIG. 78) as acel/decel noise, the record is checked at thepoint of threshold crossing for a narrow spike; if one exists, therecord is degraded.

The acel/decel subroutine is reached in FIG. 56 through an entry point1, and a series of steps 2 set up the conditions to look for a verynarrow spike by calling the width/peak subroutine 3: the beginningsample is set as the sample of record threshold crossing; the widthA.G.C. is set; and the threshold is set equal to the width threshold ofTable 9. As described with respect to FIG. 14, the width/peak subroutine3 is run first to find the peak value of the primary pulse, after whichthe A.G.C. width threshold is calculated internally as a functionthereof, and then the width at the A.G.C. level is found in a secondpass therethrough. This relative width is a better measure of theundesirable narrow spike than a fixed threshold width would be. When thewidth/peak subroutine 3 concludes, the width at the A.G.C. thresholdcrossing is checked in a test 4 to determine if it is less than a widthlow limit of Table 9. If it is, an affirmative result of test 4 reachesa step 5 in which the record is degraded by a width degrade factor,which is seen in Table 9 to be 40% of the maximum degradation. Then aseries of steps 7 establish the conditions for testing the record forR.M.S. noise by calling the R.M.S. subroutine 8: the beginning sample isset to one sample higher than the end of the pulse found in thesubroutine 3, and the end sample is set equal to the maximum sample.After calculating R.M.S. in the subroutine 8, a series of steps 10establish the conditions for determining the number of zero crossings bycalling the zero crossing subroutine 11: the beginning sample is setequal to the first sample of the record (the end sample remains themaximum sample as set in steps 7); and a threshold is set equal to thezero crossing threshold of Table 9. After the zero crossings aredetermined, a series of steps 12 set up the conditions for degrading thesample record on the number of zero crossings by calling the degradesubroutine 13. Then a series of steps 14 set up the conditions fordegrading the sample record on the R.M.S. noise level by calling thedegrade subroutine 15. And the quality factor, Q, is calculated in astep 16 as unity minus the ratio of the three components of degradationto the maximum degradation permitted for this category. If thedegradation is excessive, an affirmative result of a test 17 will reacha step 18 wherein the Q for the present category is set equal to zero.Otherwise, a negative result of test 17 reaches a step 19 wherein Q forthis category is set equal to the value of Q determined in step 16. Andthen, the calling program is reverted to through a return point 20.

First Embodiment--FIG. 81

Distress analysis in accordance with the present invention is achievedby summing (across an entire classification group of M+N records, foreach probe), the number of times (referred to as "count", hereinafter)that any given category has been chosen as appropriate for the samplerecord. It then determines, for each probe, which category, if any, wasidentified the maximum number of times, and causes that maximum categoryto be the category indicative of engine distress (or other cause) forthat probe for the group of records which have been classified. And, thenumber of times that the prevalent category was selected and itscategory number are stored for each probe. Thus, only about eight bitseach for three probes can summarize a whole group of M+N (e.g. 30)records that originally contained on the order of 128, 8-bit bytes ofdata. The distress analysis routine is reached in FIG. 81 through anentry point 1 and a first test 2 determines if distress analysis hasbeen requested by step 26, FIG. 9; if not, the routine ends at a point3. Otherwise, a step 4 sets the probe counter equal to zero. In theiterative part of the program, a series of steps 5: set a group counterequal to zero; set a local maximum count equal to zero; set the R'pointer to the record just preceding the beginning record of the group;advances the P' pointer so that it points to the first probe (initially,and subsequent probes in further iterations); and sets counters forfifteen categories equal to zero. Then in steps 6, the category (C) isset equal to zero; and the R' pointer is advanced to point to the nextrecord (the first record of the group, initially). A test 7 determinesif the category in record R' for probe P is the same as the categoryrepresented in the C counter (that is, for the very first test in thevery first pass, is the category, that has been selected for probe 1 inthe present record, category 1). If it is, a step 8 increments a counterfor category C. Otherwise, step 8 is bypassed. Then the category counterC is incremented in a step 9 and a test 10 determines if all of thecategories for the probe under test have been tested or not. Since thecategories include C MAX+1 (the additional one being the unknowncategory), test 10 determines if C equals C MAX for the probe, +2. Ifnot, test 7 is reverted to for the next category, etc., until all of thecategories have been tested for probe 1 of the present record. Then thegroup counter is incremented in step 11 and tested in test 12 to see ifthe end record for the present group has been reached or not. If not,the subroutine of FIG. 81 reverts to steps 6 to reset the category tozero again, and to increment R' to specify the next record in the group.Once again, all of the categories for the probe under consideration inthe second record of the group are tested to see which category wasassigned to this probe in this record. If the current setting of thecategory counter is the category assigned for this probe in this givenrecord, step 8 will increment the category counter. Otherwise, step 8 isbypassed. In a similar fashion, the entire group of records is sweptacross for the first probe, testing all the categories that the firstprobe can have, for each of the records in the group. And, the number oftimes any given category was assigned to this probe in a record isincremented in a counter for that particular category in step 8. Whenthe end record for the classification group is reached, an affirmativeresult of test 12 will reach a step 13 where the category is again resetto zero. The remainder of the subroutine simply determines whichcategory had the highest count in the group for the given probe underconsideration. It does this by a test 14 determining if the counter forcategory zero has a count equal to or less than the previouslyestablished maximum count. For category zero, (meaning the threshold wasnot exceeded in that particular case, as set in FIG. 9) test 14 iscompared against a maximum count of zero since it is reset in steps 5.Thus, if no counts were made for category zero, test 14 may beaffirmative. But in the general case, at least some records of a groupwill probably have a no-record indication so that test 14 will benegative and a set of steps 15 will set the count for group G', probe P'equal to the value in the counter for category C; the category for thisgroup and probe is taken to be the category identified by the categorycounter, C; and the maximum count for further testing is updated toequal the count of counter C. Then a step 16 will increment the categoryand a test 17 will determine if the counter now exceeds the maximumnumber of categories, +2. If not, test 14 is reverted to and the valueof the counter for the second category is compared with that establishedfor the maximum count established either in steps 5 or steps 15 in theprevious iteration. If the count for category 1 exceeds the count forcategory zero, test 14 will be negative and the steps 15 will update thecount for the probe to that established for category 1 (counter C); setthe category for this probe in this group equal to category C; andupdate the maximum count to the setting of counter C.

In the foregoing fashion, the counts for all categories for theparticular probe under consideration across the entire record arecompared, and the one with the highest count will be the countestablished in steps 15 and the category related thereto. When all thecategories, including the unknown category (which is one in excess ofthe maximum category), have been tested, test 17 (FIG. 81) will beaffirmative reaching a test 18 to determine if all probes have had theircategories summed across the entire group of records. If not, thesubroutine of FIG. 81 reverts to steps 5 to again set the group counterto zero; reset the maximum count to zero; reset the R' pointer to oneless than the beginning record of the group; advance the probe counter(P); and reset the counters for all the and categories to zeros. Then insteps and tests 8-10, the categories are all summed into appropriatecounters for each record, until the entire set of categories for theprobe under test has been examined for each of the records in the groupof records. Then the steps and tests 13-15 are repeated until thecategory having the maximum count across all of the records of the groupis selected, and the count and category recorded for this particularprobe and group. Finally, when test 18 is affirmative, there are sixunits of information, the category selected as prevelant, and the countthereof, for each of the three probes across an entire group.

The utilization of the present invention not only significantlyconserves the ultimate amount of data which must be recorded forsubsequent use, it further provides information as to the prevelantoccurrences, which information is significant. Thus, whenever ten timesnormal wear has been exceeded, it is usually found that nearly 90% ofall of the events will be analyzed to be in the same category, andrandom occurrences of other events will account for the other 10%. It isthis factor which renders utilization of the invention significant indetermining the actual cause of engine deterioration which is detectedby discriminated categories of electrostatic phenomena correspondinglycorrelated to engine events.

The embodiment of the invention described hereinbefore with respect toFIG. 81 utilizes waveform-classified categories summed across aclassification record group. The invention may also be utilized inembodiments which have such categories correlated first in other ways ona record-by-record basis. For instance, the integrity of categoryassignments can be enhanced before being summed across the entire recordfor each probe as described hereinbefore by a variety of means. As anexample, the categories may be correlated across the three or moreprobes within each record of the record group as described in a commonlyowned, copending U.S. patent application entitled "InterprobeElectrostatic Engine Diagnostics Correlation", Serial No. 453,964, filedcontemporaneously herewith by Rosenbush et al. Or, the integrity of theassigned categories may be improved by comparison of contiguous recordsfor a given probe prior to summation across a group of records, asdescribed in the commonly owned, copending U.S. patent applicationentitled "Contiguous Event Discrimination In Electrostatic EngineDiagnostics", Ser. No. 454,118, filed contemporaneously herewith byZwicke et al. Thus, the foregoing embodiment of the invention herein hasnot to do with the enhancing of the assigned categories, but simplydetermining statistically that an extremely prevelant category is theone to be considered as having caused ten times normal wear during anormalized wear interval.

Second Embodiment--FIG. 82-FIG. 86

The invention may also be practiced in embodiments which utilizeextremely simple concepts to provide very coarse indications of thecausation of electrostatic activity indicative of ten times normal wear.A simpler embodiment of the present invention is utilized with thesimple interprobe correlation disclosed in the aforementioned Rosenbushet al. application. The simple interprobe correlation therein takes intoaccount certain characteristics of waveshapes at one probe vs.characteristics of waveshapes at another probe that allow interprobecorrelation in a much simpler fashion than the waveshape discriminationwhich has been described hereinbefore. In general, the characteristicsdiffer depending upon whether a pocket of charge is caused by ametal/nonmetal rub (such as a compressor blade rubbing on an abradableseal), a metal-to-metal rub, or an erosion (high temperature corrosion).Although it is not fully understood nor proven beyond peradventure asyet, it is believed that metal/abradable rubs are similar to erosions. Anegative pocket theory is believed to have been proven conclusively forerosions. Under this theory, a microscopic surface burn creates a pocketof very hot particles in the 5 to 100 micron range of size. Theparticles are hot enough to thermionically emit electrons, leaving theparticles positive; the emitted electrons rapidly attach to airmolecules making negative ions. This results in a mixture of positiveparticles and negative ions, with no excess charge, as yet. However, theparticles are much heavier than the ions and have a difficult timefollowing the gas stream of the engine. The particulate matter,therefore, hits vanes, blades and other engine walls and is neutralized.But the ions, of molecular size, are sufficiently light that they mustfollow the gas flow stream through the engine. This results in a pocketof net negative charge. A noninsulated probe (such as probes 1 and 2herein) may actually be contacted by the particulate matter, prior tothe particulate matter contacting blades, vanes or other walls of theengine. As a newly formed pocket passes such a probe, the lighter ionswill not contact the probe; the heavier particles actually contactingthe probe cause the probe to be positive (the negative ions in thevicinity of the probe being masked thereby). Thus, a probe which islocated immediately downstream of an erosion will sense the erosion as avery sharp, initially positive pulse, as illustrated in FIG. 50.However, if an erosion occurs sufficiently upstream of the probe so thatnearly all of the particles can discharge to the blades, vanes and otherengine walls prior to the pocket passing by the probe, the pocket willthen simply be a group of negative ions and will cause an erosion to besensed as a wider, negative pulse as in FIG. 63 and FIG. 64. Thedifference is that the probe 2 is located immediately downstream of thesecond high turbine blade and thus senses second high turbine erosionsby impact from the particles themselves, but is more remote from thefirst high turbine, the particulates having been neutralized on theengine walls prior to reaching probe 2 when originating in the firsthigh turbine. Further, the second high turbine blade or vane erosion ofFIG. 67 is a sharp, positive pulse, but all of the erosion pulses becomenegative before reaching probe 3, as illustrated in FIG. 75 and FIG. 76.

The foregoing theory holds equally well for metal-on-metal rubs. Thedifference is that the rubs initially make a mixture of negativeparticles and positive ions. The reason for this is not yet understood.However, comparison of second high turbine rub illustrated in FIG. 66with the high turbine rub illustrated in FIG. 72 show the same polarityreversal as a consequence of the particles being neutralized at thewalls of the engine, whereas the ions being of molecular size, followthe gas flow stream and do not become neutralized. In the simplerembodiments of the invention, the foregoing considerations of theinitial pulse polarity (the polarity of the waveform as it first crossesthe threshold) are utilized together with the fact that the probes aredisplaced from each other along the flow of the gas stream. Forinstance, if a pocket of charge passes by all three probes, it may causea threshold crossing at probe 2 within a time frame (based on the 1.3kilohertz sampling rate) of between 2 and 8 samples after passingprobe 1. Similarly, it may cause a threshold crossing at probe 3 on theorder of 8 to 20 samples after causing a threshold crossing at probe 2,as shown in FIG. 82. High turbine vane erosion is illustrated in FIG.83.

Referring now to FIG. 84, a data acquisition interrupt routine of asecond, simple embodiment of the invention (as also disclosed in theaforementioned Rosenbush et al. application) is reached through an entrypoint 1 and a test 2 determines if the routine has been initialized ornot. On first power-up, test 2 will be negative reaching a series ofsteps 3 that reset 8 category counters (for 7 categories that can beidentified in this embodiment together with an unknown category); reseta record classification flag; set the probe number equal to 3; set anoise counter equal to zero; and then set the initialize flag.Thereafter, each time there is a data acquisition interrupt, theinitializing steps 3 are bypassed due to an affirmative result of step2.

In the iterative part of the data acquisition interrupt of FIG. 84, theP pointer is advanced to the next higher numbered probe (initially,probe 1) and the A/D for that probe is started in steps 4. Then a test 5determines when the conversion is complete in the A/D of the particularprobe, and a test 6 determines if a record is in progress, or not.Initially, there is no record in progress, so a negative result of test6 will reach a test 7 to determine if a record has been initiated, ornot. Initially it will not, so a negative result of test 7 reaches atest 8 to determine if the current probe is probe 1. Initially it is,and an affirmative result of test 8 reaches a step 9 to set the timeframe, T, equal to 1. The time frames T=1, T=2, and T=3, respectivelyrelate to the times at which a record having threshold crossings at allthree probes will occur for the respective probes. Thus if there is athreshold crossing at probe 1, it is defined to occur at T=1; then, ifthis is a record of an event seen by all three probes (as in FIG. 82),probe 2 should have a threshold crossing from 2 to 8 samples later whichis defined as T=2, and the third probe should have a threshold crossing12 to 24 samples after probe 1 (8-20 samples after probe 2), which isdefined as T=3. On the other hand, if the events occur downstream ofprobe 1, and therefore are only seen in probes 2 and 3, a short recordis declared so that the initial threshold crossing at probe 2 occurs inT=2, and within 8 to 20 samples later, a threshold crossing for probe 3will occur in T=3 (as in FIG. 83). Following step 9, a test 11determines if the digital value at the given probe is greater than apositive threshold for that probe; if so, an affirmative result of test11 reaches a step 12 to set a plus flag for that probe and time frame.If not, a negative result of test 11 reaches a step 13 to determine ifthe current A/D has a value less than the negative threshold for theparticular probe in question. If so, a step 14 sets a minus flag for theparticular probe and time frame. If not, a negative result of test 13reaches a test 15 to determine if all three probes have been sampled ornot. If not, the routine of FIG. 84 reverts to steps 4 to advance theprobe pointer to the next probe and start its A/D. Assuming no thresholdcrossing has occurred for the first probe, no record will be in progressor initiated so that tests 6 and 7 will again be negative, but this timetest 8 will be negative. This reaches a test 16 to see if the currentprobe is probe 2. If so, a step 17 sets a short record flag, indicatingthat if there is a record it will only have threshold crossings atprobes 2 and 3 (since probe 1 did not have a threshold crossing). Andthe time frame is set to 2 in a step 18 to identify the normal timeframe for signals to appear at probe 2 (along the gas stream flow). Thenthe tests 11 and/or 13 are repeated. Assuming both of them are negative,test 15 will be reached and since probe 3 has not yet been tested, itsresult will be negative as well. This causes steps 4 to be reached toadvance the P pointer and start the A/D converter for the third probe.When it is complete, tests 6 and 7 will again be negative since neitherthe first nor second probe had declared a record. This causes test 8 tobe reached and since the current probe setting is 3, there will be anegative result of test 8 as well as a negative result of test 16 sothat a step 19 sets S=24 (for reasons described hereinafter) and a step20 sets the time frame to 3. Then, threshold crossings are examined intests 11 and 13 for the third probe. This time test 15 is affirmativereaching a test 21 to determine if a record has been initiated or not.In the example being considered, no record has been initiated so anegative result of test 21 will cause the data acquisition interruptroutine of FIG. 84 to end at a point 22.

In the next data acquisition interrupt (about 80 milliseconds later, atthe 1.3 kilohertz sampling rate), assume that there is a thresholdcrossing for probe 1. This causes one of the flags to be set for probe1, time 1 in one of the steps 12, 14. And then a test 23 is reached todetermine if a record is in progress. Initially, the record is not inprogress but this reaches a step 24 to set a record initiated flag. Thentest 15 is reached and a negative result of that causes the steps 4 tobe reached to advance the P pointer to the second probe and to start itsA/D converter. A record has not been fully declared so the record inprogress test 6 is still negative; but a record has been initiated inthe present example, so test 7 is affirmative, bypassing the initiationsteps and tests 8-9, 16-20, setting the sample number, S, equal to 1 ina step 24 and allowing probe 2 to be sampled in the tests 11 and 13while the time frame is still set at 1. If there is a thresholdcrossing, one of the tests 11, 13 will cause a corresponding step 12, 14to set the appropriate flag. This would reach test 23 which is stillnegative, and cause reenforcing of the setting of the record initiatedflag in step 24 (but since it was already set, this is irrelevant). Thentest 15 is negative causing steps 4 to advance P to the third probe andstart its A/D. When complete, an affirmative result of test 5 causestest 6 to be reached once more. The record has not yet been fullydeclared so a negative result of test 6 reaches test 7. Test 7 isaffirmative because probe 1 initiated the record; this allows the thirdprobe to be sampled for a threshold crossing with respect to the firsttime frame. If there is a threshold crossing in the third probe, it willcause one of the steps 12-14 to set an appropriate flag and again reachthe test 22 which is still negative, reaching step 23. If there were nothreshold crossings, the negative result of test 13 would cause test 15to be reached. This time test 15 is affirmative reaching test 21 whichis also affirmative. An affirmative result of test 21 reaches a pair ofsteps 25 which set the record in progress flag and reset the recordinitiated flag, and then the data acquisition interrupt routine ends atthe point 22.

As a consequence of the next following data aquisition interrupt, theprogram of FIG. 84 proceeds differently. When the first probe A/D iscomplete as indicated by an affirmative result of test 5, test 6 isreached; test 6 is now affirmative reaching a test 26 to see if probe 1is current; if so, this reaches step 27 which increments S, the samplenumber. Then a test 28 is reached to determine if a short record hasbeen declared or not. In the example given, probe 1 had a thresholdexceedance which declared the record, so the step 17 was never reacheddue to the fact that test 7 caused it to be bypassed. Therefore, test 28will be negative reaching a test 29 to determine if the current samplenumber is between 2 and 8. In the example given, the sample number hasbeen incremented (in step 27) from 1 (set in step 24) to 2. Thus, test28 will be affirmative reaching step 18 to set the time frame equal to2. This defines the permissible range of times (between samples 2 and 8)when valid data of a three pulse record can be received at the secondprobe. On the other hand, if data is received on the first probe, flagscould be set for probe 1, second time frame if in fact there continuesto be a threshold exceedance on probe 1. However, this poses no problemsince the information is simply ignored, thereby enabling a simplerembodiment (rather than complicating the issue and not recognizing athreshold crossing for probe 1 during the second time frame). If thesecond probe did not have a threshold crossing, negative results oftests 11 and 13 reach test 15 which is negative, thereby reverting tosteps 4. On the other hand, if there were any threshold crossing (eventhough it will be ignored as described hereinafter), an affirmativeresult of either test 11 or 13 will pass through one of the steps 12, 14to the test 23. Since a record is currently in progress, an affirmativeresult of test 23 will reach the test 15 to determine if all threeprobes have been sampled or not. A negative result of test 15 reverts tothe steps 4. For the second probe, when step 4 advances the P pointer tothe second probe, and its A/D conversion is complete, step 6 isaffirmative reaching test 26, which now is negative since the secondprobe is being pointed to by the P pointer. Thus step 27 is bypassed andS is not incremented. Test 28 is negative but test 29 is affirmative, sothe second probe threshold crossing is tested for the second time frame.If the second probe has a threshold crossing during the second sample ofthe record, one of the tests 11, 13 will cause a corresponding step 12,14 to set an appropriate flag. And then an affirmative result of test 22will reach test 15; if there is no threshold crossing, steps 11 and 13being negative will reach step 15, the negative result of which willcause steps 4 to be reverted to. For the third probe, the operation isthe same as for the second probe. That is, test 6 is affirmative, test26 is negative, test 28 is negative, test 29 is affirmative, so that thethird probe has its value tested for a threshold crossing for the secondtime frame in sample period 2. When all three probes have been testedduring sample period 2 of a declared record, test 15 is affirmative andtest 21 is negative causing the data acquisition interrupt routine ofFIG. 84 to end at the point 21.

During the next six data acquisition interrupts in a row, test 6 isaffirmative; test 26 will be affirmative for the first probe only,reaching step 27 which increments S; and in the example underconsideration, test 28 is negative and test 29 will be affirmative. Thusall three probes are checked for threshold crossings during samplenumbers 3-8. If any of these probes have threshold crossings in morethan one threshold period, it simply reenforces the setting of the plusor minus flag. Of course, it is possible that during samples 2 through 8a given probe may first cross the negative threshold and then cross thepositive threshold (or vice versa); however, in the case of the pulsesof interest, since probe 1 is compared only with probe 2 and probe 2 iscompared only with probe 3, it can be seen that, in the expanse ofsample numbers of interest for the higher numbered probe, there islittle likelihood of a threshold crossing phase reversal. Specifically,if the first probe declares a record, it is a full record and the verynext sample will change the time frame from T=1 to T=2. In the pulses ofinterest, such as that illustrated in FIG. 82, a phase reversal withinsamples 2 through 8 on probe 2 is unlikely. Similarly, if probe 2initiates a record, no further sampling occurs until sample 8 when thetime frame is advanced from T=2 to T=3 and there is little likelihood ofa phase reversal on the third probe within the 8 to 20 samples where itis sensed.

The data acquisition interrupt of FIG. 84 proceeds after the eighthsample with a negative result of test 29 reaching a test 30 to determineif the sample number is between 12 and 24. During sample numbers 9, 10and 11, a negative result of test 30 will reach a test 32 to determineif all three probes have been considered (although no threshold checksare made when both steps 29 and 30 are negative) and then, for samplenumbers 12 through 24, test 30 is affirmative, reaching the step 10which sets the time frame, T=3. Each of the three probes have theirthresholds compared and when test 15 is affirmative, this reaches test20 which is negative causing the interrupt routine to end at point 22.

Assuming that a record was not initiated by the first probe, then anegative result of test 8 and an affirmative result of test 16 reach thestep 12 to set the short record flag. In such cases, once the record isin progress, on each pass through the data acquisition interrupt routineof FIG. 84, test 28 is affirmative, so the threshold checks are onlymade between sample numbers 8 and 20 as a consequence of a test 34.

In the case where neither the first nor second probe initiated a record,negative results of tests 8 and 16 reach a step 19 which sets the samplenumber, S, equal to 24. In all subsequent passes through the dataacquisition interrupt routine of FIG. 84, when P is set equal to 1, test26 will reach step 27 to increment S. Thus S is automatically higherthan 24, so that test 30 will be negative in every pass of a recordwhich is initiated by the third probe. During each pass through the dataacquisition interrupt routine of FIG. 84 in which no thresholdcomparisons are made due to negative results of tests 29, 30 or 34, test32 is reached to determine when all three probes have had their A/Dsstarted, even though no thresholds were checked for these probes.Whenever test 32 is affirmative, it reaches a test 37 to determine ifthe sample number is greater than 50. In the earlier parts of eachrecord, test 37 will be negative causing the subroutine to end at point22. Toward the end of any record, however, the sample number willeventually be incremented to 50 causing an affirmative result of test37. This will reach a step 38 which starts the R.M.S. A/D and a test 39that determines when the analog-to-digital conversion is complete in theR.M.S. A/D. When the conversion is complete, a test 40 determines if theR.M.S. A/D has a value higher than some noise limit (which may or maynot be on the same order of magnitude as the probe thresholds). If apulse-like record on one or more probes is in fact in progress, thismeans that other types of phenomenon (such as a rub strip or excessiveacel/decel noise) are not involved. Stated alternatively, testing thehigh end of a record for the absence of noise is a good indication of apulse-like record on one or more of the probes. If the R.M.S. noise islower than the limit, an affirmative result of test 40 will reach a test41 to determine if the sample number has reached 70 or not. If not, thedata acquisition interrupt routine of FIG. 84 exits at point 22. If thenoise is excessive, a negative result of test 40 will reach a step 42which increments the noise counter. Then a test 43 determines if thenoise counter has incremented to some value, such as 2 or 3, and if ithas, this is taken as an indication that pulse-like waveforms are notbeing sensed, but rather gross waveforms are being sensed. Thus noclassification can be made in the present embodiment. An affirmativeresult of test 43 will reach a series of steps 44 which reset the plusand minus flags; reset the record in progress flag; and restore thenoise counter to a zero setting. But if the noise counter has not beenincremented to 3, a negative result of test 43 causes the program toexit through the end point 22. If the noise is checked from samplenumber 50 through sample number 70 with no more than two exceedances,eventually test 41 will be affirmative causing a step 46 to set therecord classification flag. This is an indication that the flag settingsof steps 12 and 14 for all three probes now comprise a record which canbe classified.

Referring now to FIG. 85, the record classification routine is reachedthrough an entry point 1 and a first test 2 determines if M, the numberof records collected in the wear interval (FIG. 5-FIG. 7 hereinbefore)is zero or not, as described more fully hereinafter. Then, a test 3determines if the record classification flag is set or not. If test 3 isnegative, the record classification routine ends at a point 36. But ifthe record is to be classified, an affirmative result of test 2 reachesa pair of steps 4 in which P and T are both set equal to 1. Then a test5 determines if a plus flag has been set for P=1, T=1. If it has, thismay be indicative of compressor metal on abradable rub as illustrated inFIG. 57. An affirmative result of test 5 reaches a pair of steps 6 inwhich P and T are both set equal to 2. Then a test 7 determines if aminus flag has been set for the second probe in time frame 2. If it has,this is indicative of compressor metal on abradable rub, as indicated inFIG. 82 for the second probe. An affirmative result of test 7 reaches astep 8 to increment a counter for a first category, C, (defined in FIG.86 as compressor metal/abradable rub). But if test 7 is negative, thismeans the two probes do not correlate to that category, and a negativeresult of test 7 will reach a step 9 which increments the counter forthe eighth category, defined as unknown.

In FIG. 85, if the plus flag has not been set for the first probe in thefirst time frame, a negative result of test 5 will reach a step 10 todetermine if the negative flag had been set for the first probe in thefirst time frame. If it had, this might be indicative of compressormetal-on-metal rub, as illustrated in FIG. 58. An affirmative result oftest 10 reaches a pair of steps 11 in which P and T are both set equalto 2. Then a test 12 determines if a positive flag has been set for thesecond probe in the second time frame. If it has, this may be indicativeof a rub pocket (such as that illustrated in FIG. 72 and FIG. 73) beingsensed on the second probe (not otherwise illustrated herein). Thus anaffirmative result of test 12 will reach a step 13 to increment acounter for a second category in this embodiment, which is identified inFIG. 86 as compressor metal-to-metal rub. But if the plus flag has notbeen set for the second probe in the second time frame, a negativeresult of test 12 reaches the step 9 to increment the unknown counter.

In FIG. 85, a negative result of test 10 reaches a pair of steps 14which set P and T both equal to 2. Then a test 15 determines if the plusflag has been set for the second probe during the second time frame. Ifit has, this may be indicative of either first high turbine rubillustrated in FIG. 65, or second high turbine blade or vane erosion asillustrated in FIG. 67. To determine which, if either, of these may haveoccurred, an affirmative result of test 15 reaches a pair of steps 16which set P and T both equal to 3. Then a test 17 determines if thepositive flag has been set for the third probe during the third timeframe. If so, this may be indicative of one of the turbine rubcategories illustrated in FIG. 72, FIG. 73 or FIG. 74. In such case, anaffirmative result of test 17 will reach a step 18 to increment acounter for a third category identified in FIG. 86 as first high turbinerub. If test 17 is negative, however, that will reach a test 19 whichdetermines if the minus flag has been set for the third probe in thethird time frame. If it has, this may be indicative of one of theturbine erosions illustrated in FIG. 75 and FIG. 76. In such case, anaffirmative result of test 19 reaches a step 20 which increments acounter for a fourth category identified in FIG. 86 as second highturbine erosion.

In FIG. 85, a negative result of test 15 reaches a test 22 to determineif the minus flag has been set for the second probe in the second timeframe. If it has, this may be indicative of either of the erosionsillustrated in FIG. 63 and FIG. 64, or it may be indicative of secondhigh turbine rub illustrated in FIG. 66. In such a case, an affirmativeresult of test 22 reaches a pair of steps 23 wherein the probe and timeframe are both set equal to 3. Then a test 24 determines if the plusflag has been set for probe 3 during the third time frame. If it has,this may be indicative of one of the turbine rubs illustrated in FIG.72, FIG. 72, or FIG. 74. In such case, an affirmative result of test 24reaches a step 25 to increment a counter for a fifth category identifiedin FIG. 86 as second high turbine rub. But if not, a negative result oftest 24 reaches a test 25 which determines if a minus flag has been setfor the third probe in the third time frame. If it has, this may beindicative of one of the high turbine erosions illustrated in FIG. 75 orFIG. 76. In such case, an affirmative result of test 26 reaches a step27 which increments a counter for a sixth category identified in FIG. 86as first high turbine erosion. But if not, a negative result of test 26reaches step 9 to increment the unknown counter.

In FIG. 85, a negative result of test 22 reaches a pair of steps 30which set the probe and time frame equal to 3 and a test 31 determinesif the plus flag has been set for probe 3, time 3 in the absence of anyother probes having pulses. If so, this could only be a low turbine rubillustrated in FIG. 73, because it occurred downstream of probe 2. Insuch a case, a step 32 increments a counter for a seventh categoryidentified in FIG. 86 as low turbine rub. But if test 31 is negative,this reaches the step 9 to increment the unknown category counter. Thusregardless of what the circumstances are, if record classification is tobe performed, one of the incrementing steps 8, 13 . . . 9 of FIG. 85will be reached, after which a series of steps 33 will reset the plusand minus flags that are set in steps 12 and 14 of FIG. 84 and utilizedin FIG. 85; reset the record in progress flag so that a new record maybe obtained; and increment the M counter (as described more fully withrespect to FIG. 7 and FIG. 8 hereinbefore). Then a test 34 determines ifM has exceeded the distress threshold; if it has, an affirmative resultof test 34 reaches a step 35 to set the distress analysis flag;otherwise, step 35 is bypassed. And then the routine is ended at thepoint 36.

As described hereinbefore, if M becomes reset at the end of a wearinterval prior to reaching the distress threshold, counting of recordswill begin anew. When this occurs, all of the category counters 8, 13 .. . 9 of FIG. 85 must be reset. Therefore, whenever the recordclassification routine is entered, if the test 2 is affirmative, thisreaches a step 40 which resets all of the counters for categories 1through 8. Whenever the record classification routine is entered and noclassification has been ordered, a negative result of test 3 will causethe program to end at point 36.

Referring now to FIG. 86, the distress analysis routine is reachedthrough an entry point 1 and a first test 2 determines if distressanalysis has been ordered by the subroutine of FIG. 85, or not. If not,the routine simply ends at a point 3. But if so, a local value, C MAX,indicative of the category with the highest count, is initialized atzero and a category counter, C, is set equal to zero in a seriesdetermines if the counter for category C is higher than C MAX, and anaffirmative result of test 6 will reach steps 7 wherein C MAX is setequal to the setting of counter C and the category, CAT, is set equal toC. Otherwise, steps 7 are bypassed. Then a test 8 determines if all 8category counters have been considered. If not, the steps and tests 5-7are repeated. Eventually, all eight categories will have beenconsidered, and the category (CAT) will be set equal to the categorynumber having the highest count in the counter. An affirmative result oftest 8 reaches a test 9 to see if the category is 1. If it is, anaffirmative result of test 9 reaches a step 10 wherein an indicator, aflag or some other utilization device is set to indicate that theabnormal wear which did occur during a wear interval was determined tobe compressor metal on abradable rub. If test 9 is negative, a test 11determines if the category is 2. If so, a step 11 causes an indicationof compressor metal-on-metal rub. If test 11 is negative, a test 13determines if the category is 3. If so, a step 14 provides an indicationthat the abnormal wear is first high turbine rub. If test 13 isnegative, a test 15 determines if the category is 4. If so, a step 16provides an indication that the abnormal wear is second high turbineerosion. In a similar fashion, a plurality of tests 17-20 determine ifthe category is 5-8 and if so, set a corresponding indication 21-24. Ifsomething goes wrong, and test 20 is negative, then an indication ofsystem error may be provided in a step 25. And then G is incremented andthe distress analysis flag is reset in steps 26, and the program endsthrough the point 3.

Thus in this simple embodiment, only the likelihood of the electrostaticactivity relating to certain categories of causal engine events issummed across a record created during a period of abnormal wear. A moresophisticated statistical correlation of the likelihood of any recordrepresenting a category of engine or other events is set forth in thethird embodiment hereinafter.

Third Embodiment--FIG. 87-FIG. 88

In this embodiment of the invention, statistical correlation isperformed by combining the quality factors (Q) determined for eachcategory of each record of each probe before the category for the probeis chosen. That is to say, instead of choosing a category for each probefor each record, the categories for each probe are chosen only acrossthe multi-record group (on the order of twenty or thirty records). Thecategories assigned for any given probe are therefore representative ofcategories relating to an entire group of records, utilizing the qualityfactors assigned on a record-by-record basis, for each probe. The recordclassification described hereinbefore with respect to FIG. 9 takes oneprobe at a time, runs through the first probe subroutine first, thesecond probe subroutine next, and the third probe subroutine last. As itpasses through each of the probe subroutines, values of Q are assignedfor each potential category for that probe. And then a decision is madeas to the predominant category in that probe, if any. That becomes theassigned category for that probe in that record. When a category hasbeen assigned for each probe in a record, the next record is taken inturn. Ultimately, a full group of records has three categories assignedto each record, each category relating to one of the probes.

In the present embodiment of statistical correlation, a recordclassification routine set forth in FIG. 87 is quite similar to that ofFIG. 9 except it is performed horizontally rather than vertically, in asense. That is, each of the three probe routines are run in order toassign values of Q to each potential category for that probe.Thereafter, the like categories are geometrically summed across all ofthe records of a group, one category at a time. Thus, the first categoryfor the first probe in the first record is summed with the firstcategory for the first probe in the second record, and so forth, untilthe first probe, first category has been summed across all of therecords in the group. Then the second category for the first probe issummed across all the records in the group, and so forth. When allcategories for all three probes have been summed across all of therecords of the group, then the decision process takes place.

The record classification routine is reached in FIG. 87, through anentry point 1. A first test 2 determines if the classification flag hasbeen set for the current group. If not, the routine ends at a point 3.Otherwise, a pair of steps 3a sets the maximum sample to 104 (in thepresent embodiment, although other numbers may be used); and P' is setequal to 3. In the iterative part of the program, a series of steps 4advance P' so as to point to the first probe (initially, and additionalprobes subsequently); set the record pointer, R' PTR, to the recordwhich just precedes the first record of the current group; and set agroup counter equal to zero. Then in a series of steps 5, the R' pointeris advanced; the sample buffer is loaded with the record buffer for thecurrent record and the first probe; and the sample number, S, is setequal to zero. Then steps and tests 6, 8 and 10 look for a thresholdcrossing, but if none is found, set the category equal to zero in step11; if a threshold is found, the sample number of the threshold is setin step 13 as described hereinbefore with respect to FIG. 9. Then a test14 determines that the first probe is being looked at, causing the firstprobe subroutine 16 to be run, as described hereinbefore with respect toFIG. 9. Then a step 17 increments the group counter and a test 19determines if the full group of records has been tested for the firstprobe or not. Initially, test 19 is negative causing the routine of FIG.87 to revert to the steps 5. Therein, the R' pointer is advanced and thesample buffer is filled with the record buffer for the next record inthe sequence but still for the first probe, and the sample number isrestored to zero. Again a threshold is looked for. If a threshold isfound in test 8, its value is set in step 13, and test 14 is stillaffirmative because the first probe is still being pointed to. So thefirst probe routine is run again to check the first probe in the secondrecord and assign Q values thereto, as described hereinbefore. If nothreshold is found, tests 8 and 10 cause step 11 to set the categoryequal to zero. As described hereinbefore with respect to the first probesubroutine of FIG. 10, if no Q value is assigned, it remains zero. Thenthe group counter is incremented in step 17 and tested in 18 to see ifthe full group of records have had the first probe routine run thereon.Eventually, all of the records will have had the first probe routine runwith respect thereto, so that each record has a set of Q values for allseven categories (C MAX+1 being the unknown category) of the firstprobe. When that has been completed, an affirmative result of test 19calls a correlation subroutine 21 to correlate all the Q values for thefirst probe, as described hereinafter with respect to FIG. 89 and then atest 22 is reached to determine if Q values have been assigned andcorrelated across all the records for all three probes. Initially, test22 is negative so the routine of FIG. 86 reverts to steps 4 where the Ppointer, P', is advanced to the second probe: the R' pointer is restoredto one sample in advance of the first sample of the current record; andthe group counter is again restored to zero. And then steps 5 arereached to advance the R' pointer; bring in the first record of thesecond probe; and restore S to zero. All of the steps and tests 6-14 arerepeated but this time test 14 is negative so that if a threshold werecrossed, it will reach a test 16. This time test 16 will be where Qvalues are assigned for all of the categories of the first record of thesecond probe. This process will repeat through all of the records of agroup, each time passing through tests 16 and the second probesubroutine 18, provided a threshold is crossed. When the group iscompleted, test 19 will be affirmative causing the correlationsubroutine 21 to be reached for correlating all the Q values of all thepotential categories of the second probe across the entire group, asdescribed with respect to FIG. 87 hereinafter. Then test 22 is reachedand again is negative reverting to steps 4 to set up the process for thethird probe. For each record threshold crossing with respect to thethird probe, test 16 is negative reaching the third probe subroutine 20.Thus, the Q values are assigned for each potential category of the thirdprobe for each record in the group.

When each Q value has been provided across an entire group of recordsfor all three probes, test 22 is affirmative and a pair of steps 24reset the classification flag for the present group. The R' counterupdate is equivalent to incrementing the R' counter in the same fashionas is achieved in steps 4 of FIG. 9 hereinbefore in order to keep trackof the records which have had their information removed and thereforemay be overwritten in data acquisition if required, as described withrespect to FIG. 6 and FIG. 8 hereinbefore. And then the recordclassification routine of FIG. 87 ends at the point 3.

Correlation--FIG. 88

When the Q values have been established for the first probe portion ofeach of the records in a group, the correlation subroutine of FIG. 88 isreached through an entry point 1. A first step 2 sets a categorypointer, C, equal to zero. Then in steps 4, the group counter is setequal to zero; the R' pointer is set equal to one record in advance ofthe start of the current group; and a product is initialized as unity.

In FIG. 88, the values are combined according to the generally knowngeometric summation formula:

    Qt=1-[(1-Qa)(1-Qb)(1-Qc) . . . (1-Qmax)]

After the multiple in steps 5, the group counter is incremented and atest 6 determines if the full group has had the Q's corresponding tothis particular category multiplied across the entire group of records.If not, a negative result of test 6 reverts to steps 5 to multiply thenext Q value for the next record in the sequence. When the full group ofQ values have been multiplied together in the steps 5, an affirmativeresult of test 6 reaches a series of steps 7 wherein the Q value forthis particular category and probe for the entire group is set equal tothe resultant new total Q value established as unity minus the productprovided by steps 5; and the category is incremented. Then a test 8determines if all of the categories for the probe in question have beencombined or not (including the unknown category which is designated as CMAX (P')+1). Initially, this is not the case so a negative result oftest 8 causes the correlation subroutine of FIG. 88 to revert to steps 4to repeat the process for the second category of probe 1 across theentire group of records. The steps 4 restore the group counter to zero;cause the R' pointer to point to one record in advance of the beginningof the group and the product restored to unity. Then in steps 5, the R'pointer is advanced, initially to point to the first record in thegroup, and subsequently to point to each succeeding record; the Q valueis quadratically summed with the preceding total; and the group counteris incremented. Test 6 determines that the full group has not as yetbeen summed and reverts to steps 5. In this fashion, the Q value for thesecond category of probe 1 is quadratically summed across the entiregroup of records. Then test 6 will be affirmative so that step 7 willstore the total Q value achieved as being that for this category, thisprobe and this group. The old total Q value is updated to equal the new,and C is incremented so that test 8 will determine if all the categoriesfor this probe have been processed. Eventually, all the categories forprobe 1 will have been processed and an affirmative result of test 8reaches a decision subroutine 9 which is the same as that describedhereinbefore with respect to FIG. 13. However, test 4 in FIG. 13 in thiscase compares the Q for the group, probe and category set in step 7 ofFIG. 88 with a previously determined maximum to end up with a value of Qand a category in steps 9 of FIG. 13 which relate to the entire group,rather than to a single record.

Thus far, the subroutine of FIG. 88 has taken all the categories of thefirst probe and combined the Q values thereof across an entire group ofrecords (on the order of twenty or thirty records) and determined thecategory for which the combined Q value was maximum and what that Qvalue was. Following the decision subroutine 9, the program reverts tothe record classification routine through a return point 11, and thetest 22 determines if all three probes have had their categoriescombined and a decision made, or not. Initially, not all probes havebeen tested so a negative result of test 22 causes the recorcdclassification routine of FIG. 87 to revert to steps 4 to advance the P'pointer to point to the next probe and the assigning of Q values for allof the categories of probe 2 is achieved, as described before. When test19 of FIG. 87 is affirmative, the correlation subroutine of FIG. 88 isreached and step 2 therein reestablishes the category counter as zero.Then steps 4 reestablish the conditions for summing the first categoryfor the second probe across all of the records, steps 5 and test 6causes the Q value to be combined across the entire group of records forthe first category of the second probe. Then steps 7 preserve the Qvalue so combined for the current category; establish the old total Q asequal to the new total Q; and increment the category counter. Thisrepeats until all the categories of the second probe have had their Qvalues combined. Then test 8 will be affirmative causing the categorywith the highest value across the entire group of records to be selectedby the decision subroutine 9. Then the program reverts to FIG. 87 andtest 22 determines if all three probes have had all of their Q valuescombined and a decision made. Eventually they will have, so anaffirmative result of test 22 will cause the classification routine ofFIG. 87 to end at point 3.

The present embodiment of this invention has been described as usinggeometric summation in step 5. However, so long as Q values in excess ofunity can be tolerated, arithmetic summation may be used, if desired. Infact, in some cases it may be preferred because Q's of interestingcategories will have summation values on the order of 10-20, and permiteasy human recognition and comparison. In fact, arithmetic summationfollowed by a threshold test, to eliminate categories that do not occur,e.g., 15 out of 30 records, could be very useful.

The invention is disclosed herein as discriminating, to a highprobability, each of the exemplary signals herein from the othersherein, using the waveform discrimination of our aforementionedapplication, and in a simpler fashion by not accommodating precisediscrimination against waveshapes. The invention may be practiced in asystem which can discriminate many more types of signals than the numberdisclosed herein. The invention herein is shown as including a number offeatures which are not essential to the practice of of the presentinvention. Some of these features are disclosed and claimed in other,commonly owned, copending U.S. patent applications, and some of thefeatures are not. As an example, a normal wear interval is disclosedherein as being related to the integral of R.M.S. noise as disclosed ina commonly owned, copending U.S. patent application entitled"Normalizing Engine Wear Indication With R.M.S. Noise", Ser. No.453,966, filed contemporaneously herewith by Rosenbush and Couch; ifdesired, the wear integral may be established as a function of D.C. ioncurrent in the exhaust and the time derivative of the square of enginefan speed as described in the aforementioned Couch article. Theinvention is disclosed herein as incorporating the twenty millisecondcyclic history of data disclosed and claimed in a commonly owned,copending U.S. patent application entitled "Pulse Record Data CaptureFor Electrostatic Engine Diagnostics", Ser. No. 454,123, filedcontemporaneously herewith by Rosenbush and Couch; however, depending onthe particular data processing apparatus employed to implement thepresent invention, and particularly with suitable storage, the waveformdiscriminated engine diagnostics of the invention may be practicedutilizing other means for presenting the necessary information, eitherby preserving the information in a variety of storage schemes, orotherwise. The invention discloses use of a variable threshold of thetype described and claimed in a commonly owned, copending U.S. patentapplication entitled "Electrostatic Engine Diagnostics With AccelerationRelated Threshold", Ser. No. 453,962, filed contemporaneously herewithby Rosenbush and Couch; on the other hand, a fixed threshold, determinedon a test-by-test, engine-by-engine, or other basis, or a variablethreshold dependent upon current R.M.S. noise level, as described in theaforementioned U.S. Pat. No. 3,775,763, may be utilized if desired inconjunction with the present invention. The embodiment herein includesthe "M+N" groups of records disclosed and claimed in a commonly owned,copending U.S. patent application entitled "Expanded ClassificationSample In Electrostatic Engine Diagnostics", Ser. No. 453,967, filedcontemporaneously herewith by Couch as an analysis set. Other sets ofbefore "warning" and after "warning" quantities of records can be usedto practice this invention.

The invention is disclosed herein as utilizing a variety of probesdisposed at a variety of points in the gas stream of a gas turbineengine. The invention may be practiced using a rod probe of the typedescribed and claimed in a commonly owned, copending U.S. patentapplication entitled "Gas Turbine Access Port Plug Electrostatic Probe",Ser. No. 454,113, filed contemporaneously herewith by Shattuck et al;but other rod type probes may be utilized if desired. The exhaust probedisclosed herein is of the type disclosed and claimed in a commonlyowned, copending U.S. patent application entitled "NoncontactElectrostatic Hoop Probe For Combustion Engines", Ser. No. 432,507,filed Oct. 4, 1982 by Couch; however, the invention may be practicedutilizing other probes disclosed in said Couch application, or eitherthe grid or the ring or both described in the aforementioned Coucharticle. The invention may be utilized with still other types of probes,such as that disclosed in a commonly owned, copending U.S. patentapplication entitled "Afterburner Flameholder Ion Probe", Ser. No.454,116, filed contemporaneously herewith by Couch.

The invention may be practiced utilizing a single probe, or any numberof probes, in dependence upon the particular use to which the inventionis to be put. The invention is described as it may be implemented inground test equipment, employing a free standing hoop probe disposed aftof the engine, but it is readily implemented in a manner suitable forairborne use, to monitor the engine (with or without additionalengine-responsive apparatus and/or functions) while the aircraft is inflight. The aspects of the invention relating to the hoop probe areparticularly useful singly, since absolutely no probe need be attachedto the engine in order to employ them; it is therefore anticipated thatimplementations of the invention employing only a probe responsive tothe exhaust of the engine, separate from the engine, may find wideutility.

We claim:
 1. Electrostatic diagnostic apparatus for distinctlyrecognizing different events occurring in an operating gas turbineengine, comprising:electrostatic signal means, including a probe to bedisposed in the gas stream of an engine, for providing, when said probeis disposed in the gas stream of an operating engine, a probe signalhaving a waveshape defined by amplitude variations thereof across a timeinterval of a given duration in response to electrostatic charge flowingin the gas stream in the vicinity of said probe; an analog to digitalconverter connected for response to said electrostatic signal means; andsignal processing means connected to said analog to digital converter(a)for causing said analog to digital converter to sample the probe signalprovided by said electrostatic signal means in a manner to provide arecord of digital signals indicative of the amplitude variations thereofdefining the waveshape thereof, (b) for storing, in response to theamplitude of one of said digital signals being in excess of a thresholdmagnitude, a record comprising a contiguous sequence of said digitalsignals sufficient to define the waveshape of said probe signal,repetitively, to provide a classification group consisting of a givennumber of said records, (c) for selectively providing, for each of saidrecords, a particular engine event identifying signal selected, inresponse to said amplitude variations across said time interval, fromamong a plurality thereof, each said identifying signal corresponding toa related one of a plurality of engine events, in dependence on thewaveshape of said probe signal having characeristics correlated to anengine event corresponding to said selected engine event identifyingsignal, and (d) for providing a particular engine event category signal,for said group, correlated to an engine event corresponding to the oneof said engine event identifying signals provided for the greatestnumber of records in said group.
 2. Electrostatic diagnostic apparatusaccording to claim 1 wherein said signal processing means(a) provides,for each of said records, a particular engine event quality factorsignal corresponding to each of said engine events, (b) provides saidparticular engine event identifying signal for each of said records independence upon the engine event identified as most likely by saidquality factor signals, and provides said particular engine eventcategory signal for said group corresponding with the engine eventrelated to the engine event identifying signal assigned to the greatestnumber of said records in said group.
 3. Electrostatic diagnosticapparatus according to claim 1 wherein said signal processing meanscomprises means(a) for providing, for each of said records, a qualityfactor signal corresponding to each of said engine events, each qualityfactor signal being an indication of the likelihood of the waveshape ofthe signal represented by the corresponding record correlating to one ofsaid engine events, (b) for combining said quality factor signals foreach engine event for each of said records so as to provide a qualityfactor signal for said group for each of said engine events independence upon the quality factor signals of each of said records insaid group, and (c) for providing for said group said particular engineevent category signal correlated with the engine event for which saidgroup quality factor signals indicate the greatest likelihood of saidgroup corresponding to one of said engine events.